Notion, Classification and Procedures on Collection, Preservation and Transportation of Traces Caused by Explosion

29 November 2016


Trace materials located at the scene of explosion are one of the most critical zones during investigations. Therefore, it is not a rare occasion that some of very important trace materials and facts found affect the end result of the case at the court in an essential way. For these reasons, with the development of scientific aspects of forensic sciences, more attention is to be given to the discovery and preservation of the integrity of the evidence which are to be studied later by the subject matter experts in the criminalistic laboratories. One of the most mistaken approaches to this issue, which is related with the modern apprehension of the forensic science, is that this field is sometimes tied with the work of criminal laboratory’s technicians only, which in reality presents a major mistake. It is a fact that the skills of a laboratory technician to provide justifications on scientific basis are largely dependent from the observation, collection and evidence recording at the scene of a criminal event, because the criminalists located at the scene is to the same extent part of the forensic science, also as experts in the laboratory. If trace materials are not managed properly, the work of the criminalistic laboratory can be questioned to a great extent. This is one more reason that requires attention, both at the  scene  and  at  the  entire  routing  until  the  trace  material obtains a judiciary epilogue.

Key words: Trace materials, scene, evidences and forensic laboratory.



The scene is a material frame within which a criminal act took place, and is considered as the most important source of information. Therefore:

1)      “The criminal scene not only needs to be protected but be guarded as well. In accordance with one of the basic principles of criminalistics that the criminal act is the mirror,  reflection  of  the  perpetrator,  in  that  case  the criminal scene is presented as a starting point and completion of criminal investigations. The consequences of the criminal act as a realistic presentation in the external world are found in the permanent decomposition, and not in a tranquil position. Thus, every significant delay in protecting the scene is a vitium artis action”.

Basic and first action is securing the scene of explosion quickly and efficiently in order to preserve traces, both because of traceologic entropies and because of the fact that there are high temperatures at the scene which in most of the cases affect the destruction of traces, up until the time when explosions’ investigator has reached the scene, many individuals have already visited the same.


2)      „due  to  the  risk  of  causing  new  explosions  and  fires, respectively due to high temperatures, toxic leakages and other harmful emissions (e.g. radioactive rays) checking the scene cannot be started immediately, instead this takes place after a certain time period, whilst not seldom the scene checking needs to be accompanied with the use of

Because of the afore-mentioned reasons, verification of the material situation and its interpretation requires subject matter experts in the scene checking team, which could as a consequence lead to a change of the existing situation at the place where the incident happened.“.

3)      It  would  be  desirable  for  the  scene  to  remain  in  an unchanged situation and form until the scene checking team arrives. But we must not forget here the intervention for rescuing injured people, because «not seldom at the scene where checking is taking place, injured and dead people can be found, who are to be taken care of or addressed to health institutions. This action holds priority before the traceologic reasons due to humanity“.

But when the moment comes to act with the trace from the scene of explosion, procedures concerning collection, preservation and transportation of traces to the forensic laboratory come into question, as well as any other handling of traces until they are turned into a judicial epilogue.


Notion and classification of trace

4)    During past recent years police institutions in the entire world are ever more dependent on the forensic laboratory results4 fore collection of evidences which are otherwise unreachable from other sources. While sizing up the scene and during the checking, prosecutors, official authorized personnel, investigators, forensic technicians as  well  as other professional personnel at the scene are usually those who decide that which type of evidences (traces) shall be collected  and  how  many  units  shall  be  given  to  the forensic laboratory for analysis.

By traces according to Modly D. and Korajlić N.

„today we imply, in criminalistic terms, material changes in the objective reality which are known and which have been caused in relation to or during the committing or under preparation of a criminal act and which have a certain proving value in identifying criminalistic procedures. Traces maybe created or caused by the activity of humans, animals or objects. The issue is about the material changes in the objective reality in rapport with their current situation prior to those changes, also before committing or attempting to commit a criminal act“.

Traces are to be known to the body undertaking the procedure; it means that they are to reflect to its consciousness. Traces  may  be  material  and  non-material,  or  of  the  ideal nature.7 The latter are the traces in people’s memories, “written” as engraving in the gray layer of the brain.

Material changes in the objective reality, which are considered traces in the criminal terms, may be created at the criminal scene, on the assaulted object, on the body, on persons’  clothes and footwear, at any place that is in relation with the criminal act, in all stages of it doing. The trace is a frequent notion in criminalistics that includes traces created with the pressing of the trace receiver (mark traces, hump trace), traces created with the pressing onto the trace receiver (mark traces, photographs, reflection), traces caused by cutting, breaking, throwing and similar and separate traces created with the separation from the entirety that they belonged to.

Scientific concepts of traces as a reflection (trace reflection) of the external structure are based on certain viewpoints. Every mutual action between the objects, appearances and processes is expressed with the exchange of information (contact theory – trace contacts8), so thus between this action in most of the cases micro traces do appear.

Taking into account the variety of objects and occurrences there are of course different information. From specifying objects, occurrences and rapports comes the type of mutual action of one towards the other. Objects affecting to one another may hold active or passive role or at one moment in the first and the other in the second (at one moment it acts on them while on the other they are under counteraction).

Nevertheless, for making a change in the material world a trace, in the criminalistics aspect the following criteria are to be met10: as far as criminalistics (and criminal justice) they must be relevant, which means that the trace needs to be in relation with the criminal act, the question has to be for the material change and that the change must be adequate for identification or at least for grouping.

Nevertheless,  it  is  not  unusual  while  reviewing  general issues of the evidences, in foreign criminalistics literature, definition of objects and traces as material evidences are not taken as a specific issue. Most often the general notion of the material  evidence  is  defined,  thus  the  entire  material  side connected  to  the  act  of  crime,11   respectively  as  every  solid substance,  semi-solid  or  liquid,  even  with  fine  microscope which can serve for the verification of the truth during the investigations.12 It is also emphasized that these evidences have their form and mass, therefore can be touched and sniffed,13 seen and measured. Practically this means that these evidences can  be  discovered  and  fixated  with  the  methods  of criminalistics, represented in the scene checking procedure. Many traces are provisional traces14 which „are usually discovered by a policeman who responded first to the call, or the first witness at the scene and are to be marked and recorded as soon as possible”.

The issue is mainly about the material changes caused by the criminal act occurred, whereby the selection of methods to discover them, ascertain and elaborate during the checking of the site need to be adequate not only with the nature of changes occurred but also with their importance, respectively the envisaged connection, known and verified with the concrete object, respectively of the trace with the occurrence, as well as the manner of action of that evidence in that connection. In compliance with this, the complexity of the action in doing the scene checking is noticed not only with the quantity of objects and traces but also with many differences between them.

To this end, relevant objects found at  the scene of  crime which are later refined by the criminalistic technicians most of all are: objects of committing, objects created in connection with the criminal act; objects on which traces concerning the occurrence are found; objects indicating the identity of the perpetrator, victim and other accomplices, their activities, time of committing, mode of committing and other circumstances of the occurrence.

Special care is to be given to the objects (in which relevant criminalistic and criminal justice traces are found), and especially to those that are permanent potential hazard for the safety of the scene seeing members and for other official personnel that would eventually come in contact with them (weapons, hazardous means, poisons, psychoactive substances etc.), both at the moment these objects are found, but also when fixated, preserved and transported. Of course in that occasion other traces will be found as well such as: fingerprints, footprints, marks of car tires, blood marks and similar, but we shall not treat these traces in this work.

Many authors classify traces in different ways, but it is entirely acceptable for our needs the division provided by Vrdoljak A., Palečat R., Zorić Z.,17 whereby explosion traces may be divided in: explosive substance trace, traces from the damages caused by an explosion, primary fragments and traces pointing to the perpetrator. Division in the same way was made by Yallop H. J. as well.


2.1. Explosive substance traces

The most important step in discovering and analyzing explosive leftovers is collection of  respective samples from the scene of  explosion. No doubt that there are always explosion leftovers at the explosion scene. At the end, discovering and identification of these explosives in the laboratory would depend from the investigator’s work at the explosion scene and his abilities to perform checking of the explosion scene properly.

„Traces of the explosive substance, explosive device, igniter, trigger and other traces causes by intentional explosions at the scene, are very difficult to find and collect because they are usually mixed with soil and other debris or are distorted, chemically altered, thus making it very difficult to notice and identify them. Finding these traces requires knowledge of types of explosive devices, their parts, ancillaries, explosive features as well as possible combinations of ingredients, because very seldom can explosive substances be found at the scene and at the centre of explosion visible to our eyes. “, and can only be discovered in the laboratory. Therefore it is necessary to sieve layers from the center of explosion21 and from the near vicinity, in the sieves of different sizes. Lighting the layers may be painful and monotonous, but this is an important part of the scene reconstruction process and the cause of explosion.

Other forms of traces are so-called primary part which can be of different sizes and of different materials. Nevertheless, before the observation and taking it for expertise, such material is to be classified according to the place where it has been found and its type.

During  the  examination of  the  explosion  site,  it  is compulsory to think that the unexploded ordinance may be found in the next substance: at the center of explosion, in the material, on the edges of the damage (outer edge of the crater, penetration etc.), in the material from inside the crater, in the debris thrown from the center of explosion, in the surfaces of objects and things in the vicinity as well as primary fragments.

The largest quantities of the explosive substance traces will be in the substance part which sometime ago it was surface of the edge from the explosive device. But if the question is about using  a  smaller  amount  of  explosive,  such  traces  are  to  be sought for in about two meters distance from the explosion center. Outside that radius, inactivated explosive concentration in principle is under the detection threshold during the usage of 500 grams of TNT charge.


2.2. Damage traces caused by explosion

Seeing the damages caused by an explosion, important data may be obtained for the quantity and the type of explosion (its power and destructiveness). Thus Yallop H. J. emphasizes:

„After the explosion, the remaining parts of the explosion and decomposed products that can be identified are widely spread and may have a short duration, so it is often very difficult to find them and identify them. Nevertheless, damages caused by an explosion are easy to notice as they are permanent. Therefore, damage investigation is usually a starting point of investigating the explosion causes“.

However, it must be repeated that the explosive itself can either be condensed (solid or liquid) or dispersed (gas or dust suspension). At one time explosion may have a form of a detonation,24 and in the other a form of deflagration,25 (quick burning together with the blast).

Thus expanding from the center of explosion the shockwave together  with  primary  fragments  causes  large  and  multiple damages of buildings, objects in the building and injures the face. These damages are obvious such as:

Based on these damages we can evaluate the direction of shockwave spreading, explosion power, explosion type, as well as verify the place where the explosive was set.26


2.3. Primary fragments

One among important characteristics concerning the explosion is  fragmentation (a  characteristic  by  which  smaller  material parts are created –fragments). Fragments may be classified in two types, primary27 and secondary.

Creation of primary fragments can be as a side of the projected part of the explosive devices, such as military ammunitions, grenades, bombs, shrapnel and generally anti- personnel devices.

„Fragmentation effects can also be found in handcrafts which are more or less copy of military explosives. It should be taken as a general rule that some of the explosive devices, which contain characteristics by which they indicate, are made to spread fragments to a wide angle (wide spread) and it is believed to be against people. Also, fragment guided sprinkling may indicate that the device has been produced against people,but devices containing these characteristics are also used for drilling materials such as armor-plates and other metal plates. For all such devices it is a general rule that the explosive charge is contained in a normal metal containers from steel which blast in fragments of certain size and spread all over or to a certain direction as a result of explosion“.

Primary fragments are not produced only with explosive charge in metal containers. The material of any container would brake in fragments and those would blast. All of the primary fragments mentioned so far derive from a direct closed charge. However, all explosive devices contain components as an extra layer, starting from a simple ignition fuse up to the handmade time mechanisms or produced carefully. All components, after they have been set near the charge, may get very fine from the explosion and spread as individual elements. Therefore, it is the most reasonable that for every fragment coming from the explosion device to be considered as primary, and not only those that are part of the explosive wrapper. Because, „it is a known fact that even small fragments of some explosion device keep to some extent the original shape of the means used after the explosion (shape, color, thickness, characteristic details), thus according to this type and origin of the explosion, the device may be identified. Primary fragments are important traces because they indicate directly about the mode and mean of the act. The question is about the traces – fragments belonging to the explosion device (improvised or of a military origin), which due to explosion have been thrown from the explosion center“.

After they are collected, primary fragments are classified into two types: those who have characteristics that provide indications for the device and those that do not provide indications.

„Sometimes many fragments may be found, so that the whole device may be reconstructed. However, in the situations when not many fragments can be found, then one or more primary fragments can be found which indicate the characteristics from which it can be concluded over the origin of the device or of a part of it. Taking into account large number of explosive devices  produced  and  limited  opportunities  of  those handmade it is impossible to make the complete list of the diagnostic characteristics of this type. However, it is possible to determine their joint general nature. The investigator needs to construct his base on the basis of his general knowledge on explosives and continuous experience“.

Parts of the explosion device that can be found within the explosion center are as following: 1) Fragments deriving from the explosive charge wrapper (these fragments may indicate four types of diagnostic characteristics, such as: shape32, color, marks,  material),  2) Fragments deriving from the prime mechanism, detonator or the fuse,  operating mechanism, 3) Fragments deriving from the outer containers.


2.4. Traces indicating the perpetrator

In the wide surface of the scene, more accurately in the far and near circle, traces may be found which indicate directly or indirectly the perpetrator of the criminal act, that they are created by his activities during his arrival, activities during the setting of the explosive device and during the departure from the scene.39  During the scene checking, care must be taken for those traces that should not be in the immediate vicinity of the explosion center. Assessment of the relevance of such traces depends on the person’s experience checking the area starting from the fact that depends on many circumstances; no precise rule can be set.

It is important to emphasize that the traces of the perpetrator and things belonging to him can be expected. Those can be footwear marks, frilled lines,40  vehicle tire marks, intervention tools, cigarette buts, matches, parts of the clothing left behind due to the stuck to some sharp edge of the building (glass, tree branch, nail etc.) cigarette packs, buttons and similar. Also during the scene checking, care must be taken for the state and appearance of the lock/key mechanism of the entry door and window.

A good chance is required to get the explosive in unnoticeably and later on to withdraw it unnoticeably, which is usually  studied  and  resolved  carefully.  Type  of  explosive device used shall set the necessary time for the activation of the explosive device. Practice shows that bombs can be set on the scene  several  hours,  even  days  before  the  explosion.  Thus, today in the times of a mobile telephones, perpetrators have the chance to set the explosive device which would be activated with his call from a different place, even different continent, several days, months or years after the explosive device was set.

Hereby the alibi of the suspect is to be carefully verified for that time before, during and after the explosion has happened.

The suspect is to be brought to the causal relation with the explosion. Evidence would serve to this aim (explosive device and mechanism), as well as other traces which would bring up to the identification of the suspect. Therefore, the suspect is to be checked thoroughly as far as explosive traces. Dirt under the fingernails is often full of trace substance which has been used to make the explosive devices.42  Dependent on the type of the explosive  device,  changes  may  be  identified  in  color,  burnt areas and other injuries. The same applies for the suspect’s clothes.

Due to this and other reasons, the apartment, workshop and workplace of the suspect are to be checked in details, taking into consideration explosive substances such as acids, nitrates, explosive shells, igniters, explosive mass, different explosives etc. Further on suspect’s tools to be checked on which dust, paint, and different dirt can be found etc. The same applies for personal and vehicle checking taking into account the version for mentioned traces.

All evidences prior  to their movement are to be photographed where they have been found, measured and reflected on the sketch. The investigator should also check far areas like: roofs, buildings edges, trees and other areas that can contain parts of the explosive device. Due to the large number of   people  involved  in   checking  and   the   amount  of   the evidencing material collected it is useful to note every proving object including the date, place and name of the person who collected that material. The note facilitates the determination of the chain of evidences and makes the evidence recording easier.


Trace collection, preservation and transportation procedure

As the presentation of evidences at the court is traditionally the last thing that happens to the evidence, the Criminal Procedural Law requires for the evidence to be taken legally and that the status, identity and importance of the evidence to be covered before it can be used. Detailed discussion on legal assessment of collecting and using the evidence is not included but there are some basic principles that the forensic officer must take into consideration. In general the evidence is to be collected according to rules whereas the forensic officer must be authorized to be present there where the evidence has been found and must have the right to move the evidence.

In most of the cases it is useful to seek and take specific permission from the person in control of the area and the evidence. As is the case more or less with other explosive investigation cases, writing carefully and in details this aspect of investigation through photography, notes, sketches, minutes and other ways of documenting the situation at later stages of investigation would show as much important.

A large number of criminal acts in which no physical evidences have been used have not been resolved as the evidences could not be gathered and have not been studied in a qualitative way, or have not been preserved and transported in a way that would enable non-contamination of the evidence, get damaged or badly elaborated both at the scene and the forensic laboratories. Collection of these materials is a special task that requires certain amount of specific equipment and special   approach,   when   the   question   is   either   for   large evidences or for those microscopic. It even requires final and systematic procedure which can be followed in that way that nothing is left to the opportunity and it should be economic as much as possible. Special emphasis is to be given here to the quality of the forensic officer and other personnel involved in the evidence “chain of protection” or “chain of evidences”, as emphasizes Kennedy P. M. i Kennedy J.,45  it is a continuousrecording   of   the   situation,   ensuring   and   possessing   the evidence from the time when it was discovered and collected, until its final use. „The chain” is mostly set when noted in writing every time when the evidence has been used or has been examined and by whom as well.

This note shall also include information that the evidence has been kept properly in order to prevent alternation in between every use or marked examination. This is usually achieved through a special diary for the evidence furthermore for every part of the evidence.

Every use, change of location, test or examination of the evidence is written in details in the diary. Name of every individual is written who in any way has come into a contact with the trace and it is written together with the date, time and nature of the activity involving the evidence. The diary46 needs to be enriched with the photographs of the evidence before, during and after every use. If the evidence is to be changed in any   way   before   the   use,   examination,   testing,   such   as destructive testing; in that case this is to be noted carefully.

Continuous care is to be taken for the evidence not to suffer needlessly or get damaged during the preservation or transportation process for the examination purposes.47  This is often difficult to achieve because physical evidences in most of the cases are found in the soil and under tons of material damaged by the explosion. Checking of the scene of explosion which includes digging and searching, often damages the evidence. Although this is often impossible, sometimes little care can prevent further unnecessary damaging.

One of very important procedures concerning traces found is their packaging and marking, because by packaging and marking the traces, their identity and integrity is to be ensured. Dependent on the type of material, different types of preservation packaging can be used. The most adequate way is to preserve in: paper box, plastic, glass or metal container dependent on the item to be transported.

The material from the direct circle of the explosion center must be packed in a way to take into account that the explosive material  trace  can  be  found  in  that  substance  that  are  not visible. These samples are to be packed in plastic bags and closed hermetically with the glue. Metal fragments with sharp edges must be protected in a way not to damage the package e.g. wrapping the whole fragment in a white clean paper and then place it in a plastic or glass container.

By marking (labeling) the samples identity is ensured, which is very important in further investigations procedure. The sample marking (labeling) must show clearly: case name, case number, organizational unit of the agency working on the case, date and time when the sample was taken, data on the victim, data on the suspect, place from where it was collected with the mark of the photography and the sketch, location where the trace was found, name and surname and the official status of the person taking samples as well as the preservation method.

If the question is about the fragment traces that have penetrated in the material of the near objects, adequate tools are to be used to extract (knife, needle, clipper, scalpel etc.) dependent  on  the  type  of  material  that  the  fragment  is extracted.

So, the identification, collection, insurance and preservation of evidences must be undertaken in a way to protect them and reduce  the  opportunity  for  contamination  and  provides  for their safekeeping. These steps assist in proving the elements of a possible crime and provide basis for performance of full, precise and objective judicial procedure.

In other words there should be efficient, accurate and standardized methods of communications with personnel from the laboratory. Some of the most important aspects of this communications  are:  proving  material  must  be  packed  and documented properly; before it is delivered, the proving material must be in full control of the authorized person; the entire proving material needs to be documented in details on the paper which is submitted to the laboratory.

Quantity of traces and their validity is conditioned from the power of explosion and secondary thermal effect. According to a rule, the larger the device is and the smaller the fragments are, the wider is the area of their spreading.

Besides this, also known samples of object checking are to be delivered, that were at the scene during the explosion, e.g. samples of wall paints, samples of the nearby soil, carpet etc.48


3.1. Equipment and tools for sample collection

Several types of detectors are on sale for finding the traces of explosions. Starting from the electronic detectors, which according to their construction represent small gas chromatograph,  up  to  the  detectors  that  represent  a combination  of  absorption  pumps  and  specific  discovering tubes for certain types of explosives. Trained dogs can provide great assistance in finding the explosives.

For manual detection of the explosive’s sensitivity, a device may serve which is composed from the parts of iron with the plastered depth to  which small  metallic cylinder is  inserted with a diameter of about 1,5 cm and height about 2 cm. At the end of this depth, a small hole was drilled crosswise. Checking is carried out in that way that at the end, two suspect samples are placed from 1 to 2 mg. or a piece of wet paper with the sample. Cylinder is placed above it which is slowly hammered with a 0.5 kg hammer. If it explodes then it falls within the sensitive explosives and that specific measures are to be undertaken.

Alongside the equipment of the ordinary criminal-technical science technique which is used for work at the place of fire. Supplementary  kit  for  sample  taking  is  used  to  investigate explosives  such  as  (cotton  tampons,  gloves,  distilled  water, acetone, PVC and paper bags).49

Traces from the material which are considered to be deriving from the explosive material (residues) are to be removed mechanically from the base they are found.50  So that the removed material is placed in clean test tubes of glass or in other containers of small dimensions that need to be closed hermetically with the cork tap.51 Because of the security during transportation, it is necessary to take smaller amounts of the material, and before they are taken for examination to check the sensitivity of  the  sample material52   towards mechanical impacts.

Collecting the material which is spread in the surrounding of the explosion center is made in stages.

„Superficial surface is taken first by collecting it carefully with the shoulder-blade. Such material is to be packed specifically in the paper or plastic container (bag, box), to be marked and taken for examination. Besides this, a medium layer and lower layer sample is to be taken. They are to be packed separately and are to be marked. The quality needs to be delivered as much as possible. Always certain number of neutral soil, stones, parts of the walls etc comparison samples are to be delivered, for which it is supposed with certainty  that  they  have  not  been  affected  by  the explosion“.


Concluding remarks

Based on everything said above and analyzing the existing applicable law as well as existing criminalistics practice, we can come to some certain proposals that could improve existing situation in this very sensitive field:

ƒ Needless access to the scene is prohibited.

ƒ Authorized personnel responsible for providing security to the scene must log all visitors including the name, rank, purpose of the visit as well as the time of arrival and departure. No single undocumented visitor shall dare to approach the scene.

ƒ  Each authorized personnel must write a standard report  in which he describes his role and concrete actions that he/she was carrying out at the scene.

ƒ  All visitors of the scene must provide every requested sample (blood, hair, shoe marks, fingerprints etc), for the purposes of elimination.

ƒ  Highest ranking officially authorized personnel, at the time of approaching to the scene, must take the responsibility of all subordinated visitors at the scene. Every leader visiting the scene because of curiosity only, must stay there until the criminalistic technicians do their work or until a senior officer comes.

It must be emphasized that by these and other similar procedures, unnecessary visits would be discouraged from the scene, and that duties and obligations would flow.

The organization of the law enforcement agency should be based on the legalities of the science, practice and tradition. The work of the authorized personnel should change into a profession. In this plane the role of the professional leadership in  the  law  enforcement  agencies  and  the  required reorganization is an imperative. Technical means should serve to the operational work strategy in the organization.

Translated by Trankos