Forensics is the application of science to investigations for evidence collection, preservation, and analysis, so has a broad focus; DNA analysis, fingerprint analysis, blood stain pattern analysis, firearms examination and ballistics, tool mark analysis, serology, toxicology, hair and fiber analysis, footwear and tire tread analysis, drug chemistry, paint and glass analysis, linguistics, digital audio video and photo analysis, etc. Forensic scientists will often testify as 'expert witnesses' in trials. In addition to linking a suspect's identity to a crime, forensics is often used to link discrete crimes together.
Used in tactics: Incrimination
Fire investigations have two distinct stages: fire scene investigation, which focuses on evidence at the location of the fire, and fire debris analysis, which focuses on evidence removed from the location and analyzed in a laboratory.
Fire scene investigation is much more difficult if the 'flashover' point has been reached - where a room becomes so hot that every ignitable surface will burst into flames. This stage concerns itself with determining whether a fire was intentionally set, and identifying the point of origin of a fire.
Fire debris analysis focuses on ignitable liquid residues (ILRs) and aims to identify any potential accelerant traces and their chemical composition - these samples are generally located with dogs at the scene.
Forensic ballistics involves the examination of evidence from firearms. When a bullet is fired from a gun, the gun leaves microscopic marks on the bullet and cartridge case. These marks are like ballistic fingerprints.
If investigators recover bullets from a crime scene, forensic examiners can test-fire a suspect’s gun, then compare the marks on the crime scene bullet to marks on the test-fired bullet. Cartridge cases are compared in the same way.
With the exception of red blood cells, every cell in your body has DNA. We are constantly shedding DNA in various forms; skin cells, hair, saliva, blood, and sweat are all sources of DNA. Variations in genetic code are used to identify individuals.
Police have DNA databases for comparison purposes, often obtained during arrests or as part of sentencing. DNA has been used for identification purposes since 1985, and is often treated as a 'gold standard' during trial. DNA found at a crime scene may be partial or 'mixed' - not all samples are sufficient to make a comparison, but the required amount is decreasing with technological advancements.
Digital forensics is concerned with retrieving, storing and analyzing electronic data that can be useful in criminal investigations. This includes information from computers, hard drives, mobile phones and other data storage devices.
For example, digital forensics can be used to retrieve a 'deleted' file from a computer's hard drive, to establish web browsing history, or to determine how a server was hacked.
Facial recognition is a technology capable of matching a human face from a digital image or a video against a database of faces.
It works by pinpointing and measuring facial features from a given image - today, sophisticated facial recognition technology is capable of identifying a masked individual if their eyes and eyebrows are showing. Facial recognition paired with mass video surveillance is used to automate the tracking of identified individuals through a space. Its use as evidence at trial does not have consensus.
See the facial recognition topic.
Our skin secretes oil, which we transfer to any object we touch in the form of uniquely identifying fingerprints.
On some surfaces such as metal, an imprint can be etched into the surface itself due to the reaction between the oil and metal, causing the fingerprint to be identifiable even after the surface is wiped with an acetone soaked rag.
Police have fingerprint databases for comparison purposes, often obtained during arrests. Fingerprints found at a crime scene may be partial, distorted, or smudged - sufficient detail needs to be present to make a comparison.
See the fingerprints topic.
Gait is the way that we move, a type of behavioral biometric; gait recognition identifies people by their walking style and pace which are extremely difficult to change.
Each person’s gait can be defined by unique measurements such as the locations of ankle, knee, and hip. Gait recognition can enable the identification of people even if their faces are obscured. Advanced gait recognition technologies can identify someone at a great distance even if they intentionally attempt to change their gait.
Every person has a unique way of writing. Handwriting analysis is a process that relies on knowledge of which characteristics of letter formation are unique and the physiological processes behind writing - the ways in which a person's fine-motor skills can affect their handwriting and leave clues about the author's identity.
Forensic linguistics are used for author identification (stylometry); such identification relies on analysis of particular patterns of language use (vocabulary, collocations, spelling, grammar, etc.). Linguistics are also used for voice identification; determining if the voice on a recording is that of the suspect, through acoustic qualities.
Tiny fragments of physical evidence such as hairs (including pet hairs), gunshot residue, fibers from clothing, flecks of paint or pieces of glass are examples of trace evidence, and can be transferred when two objects touch or when small particles are disbursed by an action or movement. Less frequently included items are soil, cosmetics and fire debris.
Most test methods require magnification and/or chemical analysis. Trace evidence can be used to link people or objects to places, other people or other objects, and often serves as a lead for a particular line of investigation.
See the other physical traces topic.