Preparation and attention to detail are key to handling DNA—which could be key to a criminal law case. Topics: Forensics. Visit our training center, where you can view videos on a range of applications from food safety to microbiology.
We've compiled our content in a handy library so you can find all our best resources in one place. Stay informed about industry news, current events, and the unique properties of Puritan's wide range of products that set them apart from the rest. Home Education Blog. What is DNA Contamination? The Trouble with Touch DNA Contamination Touch DNA , the invisible cells humans transfer to everything we contact, is currently being evaluated for its potential to contaminate crime scene evidence.
The National Criminal Justice Reference Service NCJRS outlines the following tips for preventing evidence contamination: Wear gloves and change them often Use disposable instruments or clean them thoroughly before and after handling each sample Avoid touching the area where DNA may exist Avoid talking, sneezing, and coughing over evidence Avoid touching your face, nose, and mouth when collecting and packaging evidence Air-dry evidence thoroughly before packaging Put evidence into new paper bags or envelopes, not into plastic bags, and don't use staples" Crime Scene Officers should also use different tools—tweezers, fingerprint brushes and powders, swabs—at every scene.
How To Videos Visit our training center, where you can view videos on a range of applications from food safety to microbiology. Resource Library We've compiled our content in a handy library so you can find all our best resources in one place. Resource Library. The wet evidence can be placed in the drying hood with the paper container still sealed. It will dry without removal from the container. If excessively wet, the item will need to be removed from the container, dried and repackaged.
The original container must be kept to maintain chain of custody and evidence integrity. Any trace evidence that may have fallen off the evidence must be retained in the paper container. If a bloody item is to be dried in a vented hood, the hood should be decontaminated first. In addition, do not place items from different cases in the hood at the same time.
Access to and from the room where the hood is located should be restricted and monitored for security purposes. Transportation of the evidence from the scene requires special consideration to prevent destruction and contamination. Some evidence, particularly biological evidence, may be sensitive to absolute temperature or fluctuations in temperature.
During the summer months or when a vehicle is in direct sunlight, the temperature inside a vehicle can rise substantially. Placing evidence in an enclosed area of a vehicle under these types of circumstances can destroy or contaminate the evidence.
During colder times of the year, precautions to prevent freezing of the evidence should also be taken. Leakage from the evidence containers can be contained by transporting the evidence in an open top plastic container.
Provisions must be made to properly store the evidence to prevent contamination and maintain evidence security. The ability to temporarily store the evidence in a secured facility, away from other items in a temperature controlled environment must exist or the evidence must be transported to the crime laboratory immediately. Access to these areas on the weekend or after hours must also be controlled and monitored for evidence security purposes.
This is another area for potential contamination. Evidence from other cases can have a leakage problem and consequently, contaminate all evidence packages placed on the receiving counter. Decontamination of this area should be done on a repeated basis during the working hours of the laboratory.
After the evidence is properly received, it usually goes to a temporary storage vault. Potential leakage of other containers in this vault or storage area, in general, may cause contamination problems which need to be addressed. Eventually, the evidence is removed from the vault and taken to a section of the laboratory for examination and analysis. The package is now placed on a table or counter where many other pieces of evidence have been over the years.
However, most laboratories have adequate decontamination procedures already in place. The analysts are cognizant of cross contamination issues and keep their work areas decontaminated on a routine basis.
Standard procedures and policies are usually adopted by the facility and the forensic scientists to reduce the potential risk of contamination. After the evidence has been analyzed, the evidence containers are usually resealed in the same packaging or an additional package and stored in a temporary evidence vault. Eventually, the evidence is transferred to the investigating agency or retained by the laboratory for court. Transporting the evidence to storage and additional handling may also create potential contamination concerns and must not be taken lightly.
Further analysis of the evidence may be required at a later date, sometimes years later. Therefore, protective gloves should always be worn when a paper container is handled. The potential for evidence contamination has been a concern of law enforcement and forensic practitioners, in general, ever since evidence was first analyzed. However, the potential impact of evidence contamination upon the outcome of a criminal investigation has become ever more important due to the sensitivities of current scientific analyses, such as forensic DNA analysis.
If evidence is properly collected from the scene, packaged and handled correctly during transportation and storage, and decontamination procedures used, the potential for contamination will be greatly reduced. As a result, the integrity and value of the evidence will be maintained regardless of what additional analyses are developed in the future.
Continuing education and training for law enforcement and forensic specialists is required to insure the proper handling of evidence from scene to storage and ultimately, reducing the risk for contamination as well as the impact of these issues upon the outcome of a criminal investigation. Printer Friendly Page. Citations Please use one of the following formats to cite this article in your essay, paper or report: APA Rustidge, Morgan. MLA Rustidge, Morgan. Chicago Rustidge, Morgan.
Harvard Rustidge, Morgan. Suggested Reading. Researchers propose replacing ancestry in forensics with a population structure approach. Using mass spectrometry to determine the sex of fingermarks. The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoLifeSciences. Role of Analytical Chemistry in the Pharmaceutical Industry. Role of Chromatography in Environmental Monitoring. Gene Identification Tools in Bioinformatics. An Overview of Nanochemistry.
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Latest Life Science News. Improving our Understanding of Bacterial Membranes. Study examines plant-based alternative food consumption trends in the UK. Seasoning foods with herbs and spices may help improve heart health. Newsletters you may be interested in. Genomics Subscribe or Preview. These persons might include:. Any unauthorized person who enters or attempts to enter a crime scene should be challenged by the crime scene security officer, and, if that person refuses to leave, they can be arrested, removed from the scene, and charged for obstructing a police officer.
The assigned security officer is responsible for creating and maintaining the Crime Security Log, which can take various forms. Whatever the scale or format, the security log records who attended the scene, when they attended, why they were there, and when they left the scene.
An example of a crime scene security log is shown in the following example. As we have already learned in the STAIR tool, analysis is the process that must occur to establish connections between the victims, witnesses, and suspects in relation to the criminal event. The crime scene is often a nexus of those events and consequently, it requires a systematic approach to ensure that the evidence gathered will be acceptable in court.
Exhibits, such as blood, hair, fibre, fingerprints, and other objects requiring forensic analysis, may illustrate spatial relationships through evidence transfers.
Other types of physical evidence may establish timelines and circumstantial indications of motive, opportunity, or means. All evidence within the physical environment of the crime scene is critically important to the investigative process. At any crime scene, the two greatest challenges to the physical evidence are contamination and loss of continuity. Contamination is the unwanted alteration of evidence that could affect the integrity of the original exhibit or the crime scene.
This unwanted alteration of evidence can wipe away original evidence transfer, dilute a sample, or deposit misleading new materials onto an exhibit. Just as evidence transfer between a suspect and the crime scene or the suspect and the victim can establish a circumstantial connection, contamination can compromise the analysis of the original evidence transfer to the extent that the court may not accept the analysis and the inference that the analysis might otherwise have shown.
Contamination is a fact of life for investigators, and any crime scene will have some level of contamination before the scene becomes an inactive event and the police can lock down the location.
While issues of life and safety are at risk, the court will accept that some contamination is outside the control of the investigator. That tolerance for controlling contamination changes significantly once the crime scene is locked down and is under control. Once the scene has been locked down, crime scene management procedures must be put in place. Crime scene contamination presents three challenges for investigators, namely:. This practice of identifying and recording the known contamination is necessary, and even if contamination has taken place, identifying and explaining that contamination may salvage the analysis of exhibits that have been contaminated.
During the critical period between the lockdown of the crime scene and obtaining a warrant to search the crime scene, investigators need to consider the possibilities for ongoing contamination. If reasonable grounds exist to believe that evidence of the crime will be damaged or destroyed by some threat of contamination, the investigator has the authority, under exigent circumstances, to re-enter that crime scene without a warrant to take the necessary steps to stop or prevent contamination and protect the evidence.
The very act of entering the crime scene to collect evidence, and the process of evidence collection, are forms of contamination. The goal in controlling ongoing contamination is to avoid damaging the forensic integrity of the crime scene and its associated exhibits.
It is this goal that makes crime scene management procedures essential to the investigative process. Like controlling contamination, establishing and maintaining continuity of evidence are protocols that protect the integrity of that evidence. For any evidence to be accepted by the court, the judge must be satisfied that the exhibit presented is the same item that was taken from the crime scene. The evidence to show continuity will come from the investigator testifying that the exhibit being presented is the same exhibit that was seized at the crime scene.
This testimony is supported by the investigator showing the court their markings on the exhibit or its container. These markings will include the time, date, and investigator initials, as well as a notebook entry showing the time, date, and place when the item was transported and locked away in the main exhibit holding locker. This evidence is further supported by an Exhibit Log that shows the exhibit as part of the crime scene evidence detailing where at the crime scene it was found, by whom it was found, and the supporting initials of anyone else who handled that exhibit from the crime scene continuously to the main exhibit locker.
Any process where that exhibit is removed from the main exhibit locker for examination or analysis must be similarly tracked and documented with the initials, time, and date of any other handlers of the item. Any person who has handled the exhibit must be able to take the stand providing testimony that maintains the chain of continuity of the exhibit. These are simple processes yet critical.
If they are not followed rigorously, it can result in the exclusion of exhibits based on lost continuity. One of the big dilemmas in crime scene management is determining where the criminal event happened or where the event extended to. Making these determinations provides the investigator with the locations where evidence of the crime may be found. This is often not a simple matter of just attending one location or thinking about the criminal event in just a single timeframe.
In the investigative process, there are three possible stages of time where evidence can originate. These are the pre-crime stage, the criminal event stage, and the post-crime stage. These three stages of crime can also mean there could be other locations outside the immediately crime scene area where criminal activities might have also taken place and evidence might be found. The point to remember about the originating stages of evidence is that each of these stages provides possibilities for collecting evidence that could connect the suspect to the crime.
When considering theory development or making an investigative plan, each of these stages of the criminal event should be considered.
Evidence does not always appear as a fully formed piece of information that offers an immediate connection or an inference to implicate a suspect. Pieces of physical evidence often referred to as exhibits, have investigative values at two different levels for investigators.
At the first level each physical exhibit has a face value represented by what it is and where it exists within the context of the crime scene. For example a bloody shoeprint found on the floor of a crime scene tells us that someone transferred evidence of blood onto their shoe from a source and walked in a particular direction within the crime scene. These are first level interpretations of evidence that we can reconstruct with our own observations.
At the second level this same bloody shoeprint may be subjected to forensic examinations that could provide additional information. For example analysis of the shoeprint pattern, size, and accidental characteristics may allow a positive match to the shoe of a suspect, or the blood may be examined to match the DNA of a victim or other originating source. Both these first level and second level values can greatly assist in creating a reconstruction and interpretation of what happened at the crime scene.
Physical exhibits that need to be examined, seized, and documented at any crime scene are a major concern for investigators. As mentioned earlier, one of the big challenges for investigators is to identify and document all of the available evidence and information. This raises the important questions of what will become evidence and what is going to be important?
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