thumb|300px|The [[Vinland Map identified as a forgery through chemical analysis in 2018]]
Trace evidence occurs when objects make contact, and material is transferred. This type of evidence is usually not visible to the naked eye and requires specific tools and techniques to be located and obtained. Due to this, trace evidence is often overlooked, and investigators must be trained to detect it. This evidence can link a victim to suspects and a victim or suspect to the crime scene. In terms of investigative aids, trace evidence can provide information to determine the origin of a sample and determine the manufacture date of the material, all of which can limit potential suspects in a case. This statement can then be expanded by stating trace evidence must first be located and recorded before it can be recovered and analyzed. Since then, forensic scientists use trace evidence to reconstruct crimes and to describe the people, places, and things involved in them. Studies of homicides published in the forensic science literature show how trace evidence is used to solve crimes.
Examples and cases
thumb|Art forgery determined by forensic analysis of pigments
Trace evidence is found in many different forms with some examples including, but not limited, to fire debris, gunshot residue, glass fragments, and fibres. The next step in recording the evidence would be still photographs. The images included should be photos of the evidence both with flash and without, the evidence with a ruler for size reference, and the evidence with its number in the photo. Hand picking is straightforward, with the evidence being carefully picked up by hand or with forceps and placed in the proper packaging for that specific item.
Trace Evidence is also found in much smaller amounts at crime scenes.
The Scientific Working Group Materials Analysis (SWGMAT) has created guidelines to ensure proper protection and collection of trace evidence. In this document you can find steps to ensure proper documentation, tips to avoid contamination and loss of evidence, proper detection, collection, and preservation techniques, as well as considerations for specific types of trace materials.
Following these standards and guidelines will ensure accurate analysis of crime scene evidence and increase the strength of the evidence in courts.
Analysis
thumb|Close-up of broken fuel pipe using [[optical microscopy]]
thumb|Droplets of human blood. The droplets are round and show no splattering, indicating they impacted relatively slowly, in this case from a height of two feet.
The way the analysis of trace evidence is performed is dependant on the evidence being examined. Most commonly the trace evidence that is examined is microscopic due to the fact that it can not be examined by the naked eye. In this case there are many different types of microscopes that can be used including stereomicroscope, scanning electron microscope (SEM) or comparison microscope.
When it comes to impression trace analysis such as a tire track in mud or a footprint, a cast or lift may be made of the impression. Partial fingerprints are even more vulnerable to false positives. Samples from accidents or crimes should therefore be protected as much as possible by enclosure in a sealable container as soon as possible, after an incident is under investigation.
In terms of scientific research that is being conducted for trace evidence, there are many gaps and a lot that remains to be done. No standards and methodologies have been created to determine physical fit between two piece of evidence and consistency of work conducted from various analysts. Therefore, it is up to the analysts discretion to determine how likely it is that the two samples came from the same source.
See also
- Blowback, material drawn into the barrel of a firearm post discharge
- Digital traces
- Evidence packaging
- Forensic chemistry
- Forensic engineering
- Forensic materials engineering
- Forensic polymer engineering
- Forensic photography
- Forensic profiling
- Forensic science
- Locard's exchange principle, which states that when two objects come into contact, there is an exchange of material
- Skid mark