Forensic testing is the scientific analysis of physical evidence to establish facts in legal investigations. It spans a wide range of disciplines, from DNA profiling and toxicology to fingerprint analysis and digital data recovery. Each type uses specific laboratory techniques to connect people, substances, or objects to a crime scene, a cause of death, or a legal dispute. The results can identify suspects, exonerate the innocent, or reconstruct what happened during an event.
DNA Profiling
DNA testing is the most widely recognized form of forensic analysis. It works because every person (except identical twins) has a unique genetic code. When biological material like blood, saliva, skin cells, or hair with an intact root is found at a scene, analysts can build a genetic profile and compare it against a suspect or a database.
The process follows four core steps. First, DNA is extracted from the biological sample. Then it’s quantified to measure how much usable DNA is present. Next comes amplification, where tiny amounts of DNA are copied millions of times so there’s enough material to work with. Finally, the amplified DNA is run through detection methods that produce a profile, typically by examining short, repeating segments of genetic code that vary from person to person.
These profiles feed into large databases. The FBI’s Combined DNA Index System (CODIS) holds over 19.2 million offender profiles, more than 6.1 million arrestee profiles, and roughly 1.4 million forensic profiles from crime scenes. As of late 2025, CODIS has produced over 781,000 hits, helping advance more than 758,000 investigations nationwide.
Forensic Toxicology
Toxicology testing determines what chemical substances are present in a person’s body. Analysts examine blood, urine, tissues, hair, and organ fluids to detect drugs, alcohol, poisons, or other chemicals. The results help answer questions that matter in both criminal and civil cases: Was this person impaired? Did a substance contribute to their death? Is an employee or parolee complying with drug-free requirements?
The field breaks into three main areas. Post-mortem toxicology helps determine the cause or manner of death. Human performance toxicology assesses whether someone was impaired at the time of a crime or accident. Forensic drug testing covers workplace screening, athletic testing, and probation monitoring.
Labs typically start with a broad screening method to flag potential substances, then confirm results using more precise instruments. Gas chromatography paired with mass spectrometry (GC/MS) is a standard confirmation tool that can identify a substance by breaking it apart and analyzing its chemical structure. For certain compounds, liquid chromatography with mass spectrometry (LC-MS) provides even greater precision. Alcohol analysis uses a separate technique called headspace gas chromatography, which can also detect related chemicals like methanol and acetone.
Fingerprint Analysis
Fingerprint identification relies on the fact that the ridges on your fingertips form patterns unique to you, and those patterns don’t change over your lifetime. When a print is recovered from a crime scene (called a latent print), examiners follow a structured process known as ACE-V to determine whether it matches a known individual.
In the analysis phase, the examiner studies the unknown print’s quality, noting the type of surface it was found on, how it was developed, and what level of ridge detail is visible. During comparison, the examiner places the unknown print alongside a known print and looks for agreement or disagreement in specific features. Evaluation is where the examiner reaches a conclusion: identification, exclusion, or inconclusive. Finally, verification involves a second examiner reviewing or independently repeating the analysis to confirm the result. Some agencies have the second examiner work without knowing the first examiner’s conclusion, adding an extra layer of objectivity.
Trace Evidence
Trace evidence refers to small, often microscopic materials transferred during physical contact: hair, fibers, glass fragments, paint chips, soil. These materials can place a person at a scene or link two objects together.
Hair examination under a microscope can reveal whether a strand is human or animal, what body area it came from, whether it was forcibly removed, and whether a root is attached for potential DNA testing. Each hair has three structural layers (an outer covering, a middle layer of cells, and a central canal) that vary between individuals and ancestral groups. Without an intact root, DNA profiling isn’t possible, so examiners rely on these physical characteristics instead.
Fiber analysis distinguishes natural fibers from synthetic ones. Natural fibers like cotton or wool can be identified under a microscope based on their shape. Synthetic fibers require more advanced optical testing, including measurements of how they bend light and whether they fluoresce. Glass evidence is analyzed by measuring density, refractive index, color, thickness, and chemical composition, all of which can link a fragment to a specific window, bottle, or headlight.
Digital Forensics
As crimes increasingly involve technology, digital forensics has become essential. This discipline recovers and analyzes data from computers, mobile phones, storage drives, and cloud accounts. The goal is to extract information, like deleted files, messages, browsing history, or location data, and present it in a format that’s useful and legally sound.
The National Institute of Justice outlines the basic process as five steps: developing policies and procedures, assessing what evidence exists, acquiring that evidence (creating exact copies of data without altering the original), examining the contents, and documenting everything in a report. Extraction recovers raw data from the device. Analysis interprets that data and organizes it logically so investigators and courts can understand what it shows.
Chain of Custody
No forensic test result matters in court if the evidence behind it wasn’t properly handled. Chain of custody is the documented trail that tracks every person who touched a piece of evidence from the moment it was collected to the moment it’s presented at trial. Every transfer requires a log entry and a signature.
Proper documentation includes the exact location where the item was found (often with photographs), how it was packaged and preserved to protect its evidentiary value, and a complete record of every person who handled it along the way. Containers must be sealed and labeled with full identification. If there’s any gap in the chain, any sign of contamination, mislabeling, or mishandling, the evidence risks being ruled inadmissible. This procedural discipline is what separates a lab result from a legal fact.
Lab Backlogs and Processing Times
One reality of forensic testing is that results rarely come quickly. The forensic science community generally considers a case backlogged when it sits unworked for 30 or more calendar days after submission to a lab. Despite well over $1 billion in U.S. federal grant funding aimed at reducing backlogs and building lab capacity, delays persist, particularly for DNA cases. The problem isn’t simply about warehousing old cases. When new submissions consistently outpace a lab’s capacity to process them, backlogs grow regardless of how efficiently older cases are cleared. Industry data from the Project FORESIGHT benchmarking program shows that several forensic disciplines routinely receive more cases than they can complete, creating a structural bottleneck rather than a temporary one.