By way of introduction, it is appropriate to note what is said in Barry Fischer’s Techniques of Crime Scene Investigation (CRC ed. 2003) about the correct approach to the scene of a crime on the part of general non-specialist staff (Golden Rules): what to do and what not to do at the crime scene (Crime Scene Dos and Don’ts) in order to avoid basic errors and to reduce the risk of contamination.
The starting point is always Locard’s Principle , according to which two objects which come into contact with one another exchange material in different forms.
Equally, the same principle scientifically supports the possibility of contamination and alteration [of the scene] on the part of anyone else, investigators included, who comes into contact with the scene.
THINGS TO DO
- Cordon off [limitare] the crime scene (primary and secondary);
- Note any alteration of the scene due to your own intervention or that of a third party;
- Avoid introducing contamination (direct or indirect) to the scene;
- Accurately record the position of objects before moving them (attention: do not try to replace objects in their original positions);
- Pay attention to yourself as a source of pollution of the evidence.
THINGS NOT TO DO
- Permit or carry out an indiscriminate access, especially without recording it;
- Alter the condition of the sites;
- Move around without taking precautions (PPE and movement procedures);
- Fail to document access;
- Assume others will note original conditions.
It should be stressed that the Crime Scene Manager is a figure of great importance, whose task is to ensure that the operations of survey and documentation by the various components of the team proceed correctly, especially in complex crimes, and who is able to manage the emergency situation through [ensuring] the correct flow of established procedures (Crime Scene Management: scene specific methods, R. Sutton Wile, ed. 2009).
The correct procedures for cordoning off the crime scene therefore also fall within this remit, different levels of containment consequently being adopted to avoid conditions which may entail alteration of the evidence, including contamination.
It is thus crucial to mark off a more external area, intended as the ‘perimeter of containment’, followed by an area of secondary containment within and then a primary area, up to the scene of the crime itself (Crime Scene) (Increasing Crime Scene Integrity by Creating Multiple Security Levels, Greg Dagnan, Criminal Justice Missouri Southern State, 2006).
Particular attention must be paid to the floor, in that this is the most common place where evidence collects but at the same time has the biggest potential for contamination (Protecting the Crime Scene, G. Schiro – Louisiana State Police Crime Laboratory).
The Guidelines of the U.S. Department of Justice – Office of Justice Programs, Crime Scene Investigation – A guide for Law Enforcement, January 2000) appear extremely conclusive:
2. Contamination Control:
- Contamination control and the prevention of cross-contamination in single or multiple scenes is essential to maintain the safety of staff and the integrity of the evidence;
- Limit access to the scene;
- Use set routes to enter and exit the scene;
- Designate a secure area for refuse and equipment;
- Use personal protective equipment (PPE) to prevent contamination of staff and to minimize contamination of the scene;
- Clean/Sanitize or dispose of instruments/equipment and protective personal equipment between evidence collections and/or between the various scenes;
- Use disposable equipment when performing direct collection of biological samples;
- Maintain scene security throughout processing, up until the final exit from the crime scene;
- Package items in order to avoid contamination and cross-contamination;
- Maintain the evidence at the scene in an appropriate way in order to prevent its degradation or loss.
The update to the aforementioned Guidelines of the U.S. Department of Justice, Crime Scene Investigation: a Reference for Law Enforcement Training, June 2004, highlights protocols/procedures which are even more stringent:
- Designate a separate area/areas for the refuse produced in the course of the investigation of the scene;
- Establish an area/areas as a location for equipment;
- Nominate one person responsible for the removal of refuse;
- Use appropriate PPE (personal protective equipment);
- Dispose of PPE in biohazard containers;
- Use clean or disposable tools/equipment;
- Throw away disposable tools/equipment in biohazard containers or in a specialized container after use;
- Clean reusable instruments before the collection of each new piece of evidence.
The manual Handbook of Forensic Services for the Laboratory Division of the Federal Bureau of Investigation (2007) reports the following with regard to the protocols of collection, packaging and storage of DNA evidence:
- If the DNA evidence is not properly documented, its origin may be contested;
- If the item is not properly collected, biological activity may be lost;
- If it is incorrectly packaged, contamination may occur;
- If it is incorrectly stored, decomposition or deterioration may occur.
Blood on surfaces
- Absorb the suspected blood stain on a clean cotton swab. Dry the swab and package in clean paper or in an envelope with sealed corners. Do not use plastic containers;
- Allow clothing with suspected blood stains to dry. Wrap dried bloodstained clothing in clean paper. Do not put damp or dry clothing in plastic or airtight containers. Put all debris or residues from the clothing in clean paper or in an envelope with sealed corners;
- Where dried blood stains are present on immovable objects, absorb the stains on cotton swabs dampened with distilled water. Dry the swab and pack it in clean paper or in an envelope with sealed corners. Do not use plastic containers.
Storage of DNA evidence
- Store in a refrigerator, freezer (if dried), [or] at room temperature, away from light and humidity.
These recommendations on collection procedures and protocols are accepted and clearly stated in all investigative manuals:
- Evidence Field Manual, Office of Forensic Sciences, New Jersey State Police, Rel 1/08:… “Biological evidence … Blood … Thoroughly dry the stains and package in a sealed paper container, a paper bag, or wrap in clean paper … Do not use plastic containers and staples … Knives with traces of blood … (ditto) … traces of saliva … (ditto) … Fingernail swabs … dampen the swab with distilled water and swab under the nails (one swab for each hand). Air dry, package, label and send to the laboratory”.
- Forensic Evidence Handbook, Missouri State Highway Patrol, Forensic Laboratory
- North Carolina State Bureau of Investigation, Evidence Guide, January 2010: “Collection, packaging and storage of evidence:…Avoid excessive heat, humidity, and temperature fluctuations, maintaining the evidence in environmentally-controlled conditions… Allow a damp specimen or one constituted of body fluids to dry before storing. Store the evidence in appropriate containers (paper, envelopes, boxes, but not in plastic) in order to avoid the formation of condensation… Always package items in paper. Never use plastic bags… Safety considerations for biological evidence… Always follow universal precautions… Use clean gloves… Do not agitate the stain and avoid spreading fine particles which may float in the air”.
These collection methods are succinctly summarized in Protecting the Crime Scene, G. Schiro – Louisiana State Police Crime Laboratory:
Particular attention must be paid to the floor, in that this is the most common place where evidence collects but at the same time has the biggest potential for contamination.
Blood and traces of bodily fluid can be collected in the following ways: if the stained object can be transported to the laboratory, wrap it in a piece of paper or in an envelope and send it to the laboratory; if it cannot be transported, absorb the stain on material dampened with distilled water, dry it, before permanently packaging it. For transportation purposes and in order to prevent cross-contamination, the material may be put in a plastic container for no longer than 2 hours. Once arrived in the laboratory, the material must be removed from the plastic and allowed to dry. At this point, package it in a paper container and put it in a paper envelope…
Damp traces of blood and bodily fluids can be collected in the following ways: all items must be packaged separately in order to prevent cross-contamination. If the item can be transported to the laboratory, package it in a paper container (or a plastic container if the transport time is less than 2 hours), take it to a secure place and allow it to dry completely, then repackage it in a paper container. If it cannot be transported to the laboratory, then absorb the stain on a small fragment of sterile cotton. Package it in paper (or plastic if the transport time is less than 2 hours), put it in a secure place and let it dry completely; then repackage it in a paper container.
Under no circumstances can wet or damp items be left in plastic or paper containers for more than 2 hours…
This last direction must be absolutely respected, and all the protocols and procedures give specific warnings about it: as, for example, in the Physical Evidence Handbook, Department of Justice of the State of Wisconsin, State Criminal Laboratory (7th edition):
- …it needs to be ensured that the item is not altered or contaminated between the time of its collection and the time of its examination…
- items for DNA examination must always be packaged in paper or in a cardboard box, even if they appear dry…
And again, in Understanding DNA Evidence: A Guide for Victim Service Providers, Department of Justice:
…investigators and laboratory staff must always wear disposable gloves, use clean instruments, and avoid touching other objects, including their own bodies, when handling evidence. Environmental factors, like heat and humidity, can also accelerate the degradation of DNA. For example, wet or damp items which are packaged in plastic will create a growth environment for bacteria which can destroy DNA evidence. Consequently, biological evidence must be completely air-dried, packaged in paper, and correctly labelled. Treated in such a way, DNA can be stored for years without risk of degradation, even at room temperature…
The adoption of the protocols and procedures hitherto explained are universally applied not only on other continents, but also at a European level, as in the Interpol Handbook on DNA Data Exchange and Practice – Recommendations from the Interpol DNA Monitoring Expert Group – second edition 2009:
…liquid samples… If blood, semen or saliva are present as a liquid or a damp stain, they must be sampled using a dry swab or pipette. Sterile cotton swabs are available to sample stains from the crime scene. The stain must be sampled on one area of the swab, and not wiped over the entire surface of the swab tip… dry stains…: use a lightly dampened swab to sample the material for DNA, concentrating the stain in the smallest possible area [of the swab]… In all circumstances, it is important to also take a control sample… If at any point during the sampling, the sample is dropped or enters into contact with any other surface, ideally the procedure should be halted and a new disposable DNA kit used… collect clothing and gloves and dispose of them in appropriate containers…
- Due to the sensitivity of current DNA techniques, extreme caution (such as wearing a mask) must be taken if the person carrying out the sampling has a medical condition which causes the loss of bodily fluids or particles, as in the case of colds, coughs or influenza. Other conditions like eczema can require the wearing of additional clothing;
- all containers used for transportation must be cleaned before and after use or, if possible, not reused;
- the work area of crime scene staff must be regularly cleaned with wipes containing chlorohexadine;
- disposable materials should be used wherever DNA may be found;
- disposable gloves must always be worn over cuffs and should be changed for each item/sample. It is necessary to change gloves during the sampling of different items…;
- where possible, take the container to the evidence and not the evidence to the container…’
- contact between the victim and suspect samples must be avoided at all times;
- handling of the objects must be reduced to the minimum possible, and the objects must not be reopened [once packaged], not even for interrogation purposes;
- make sure that any person attending the crime scene has no contact with the suspect and with his/her clothing;
- multiple suspects, the victim and their clothing must be kept separate at all times, and must not come into contact with the same objects.
Given the importance of the correct application of inspection/collection procedures to the success of laboratory investigations, a working group called ‘Scene of Crime’ was promoted within ENFSI (European Network of Forensic Science Institutes, an organization begun in 1995 and to which 19 European countries belong) with the aim of standardizing the procedures and methods employed; guidelines were published in the Good Practice Manual for Crime Scene Management.
In Guidance on the Production of Best Practice Manuals within ENFSI, ref cod. QCC-BPM-008, 01/05/2008, the following points amongst others are highlighted:
- 4.3.2 The expert must also evaluate the risk of contamination (or any other problem which could affect the integrity of the evidence) [which may have happened] before the items provided for examination are sent to the laboratory to be examined, or before the start of the analysis…
- 5.1.1 Particular emphasis must be given in the manual to procedures for avoiding contamination, and to the advice given to assist individuals in the management of specific risks associated with the analysis;
- 5.1.3 Considerations about appropriate anti-contamination precautions must be based not only on those for the analyses under discussion, but for all types of evidence which could potentially be available. If these include materials which could be required for subsequent DNA analysis, extreme caution must be taken due to the sensitivity of current DNA techniques, by means of the wearing of appropriate clothing including gloves and face masks (see Appendix 2);
- 5.4.1. All items must be packaged and sealed as soon as they are collected, using bags or containers of an appropriate size and made of material which avoids damaging the packaging or breaking the seals;
- 5.4.2 Once sealed, the containers must not be reopened outside of the laboratory environment. If in exceptional circumstances they must be reopened, complete and detailed documentation should be drawn up as to the conditions in which they were opened.
Also from ENFSI – to which the Scientific Police Service of Rome and the Carabinieri of Rome belong – precise working directions are given in the document European Crime Scene Management: Good Practice Manual. In particular:
- …it is essential that all agents are aware of the importance of preserving the scene;
- Avoid the temptation to examine. Consider and record all contamination risks. Take down the names of everyone at the scene;
- Protect the scene: identify the extent of the scene and cordon it off. Prevent access by other people;
- Refine the most appropriate cordoned-off area. It is better that too large an area is cordoned off rather than one which is too restricted – it can always be reduced later on;
- Protect the scene;
- Establish a meeting point outside the cordoned-off area;
- Concrete and efficient channels of communication amongst those examining the scene and the team of investigators are essential in every case;
- Crime Scene Manager: Make sure that everyone who enters the scene wears protective clothing, shoe covers, masks and gloves;
- Provide advice and quality assurance on all scientific questions including the storage and collection of evidence, and withdrawal from the scene;
- Contamination: it is essential that all steps are followed to ensure there is no contamination of the collected evidence. If contamination is discovered, the results of any scientific analysis could be invalidated. Protection from contamination must always start at the crime scene and continue until the sample is deposited at the Forensic Science Laboratory;
- It is essential that each action performed in the collection of evidence is documented.
 Locard’s exchange principle states that “with contact between two items, there will be an exchange” (Thornton, 1927) and is known most commonly as the idiom “every contact leaves a trace”. Essentially, Locard’s principle is applied to crime scenes in which the perpetrator(s) of a crime comes into contact with the scene, so the perpetrator(s) will both bring something into the scene and leave with something from the scene (Wiki).