Criminology is the study of crime and criminal behavior through sociology, psychology, economics, statistics, and anthropology. Forensic chemistry sits inside that work and examines the physical evidence. The act of testing what was left behind helps investigators piece together what happened, who was present, and how events unfolded. The aim, beyond just the identification of substances, is to translate lab findings into clear narratives that can stand in court. That requires careful methods, steady documentation, and an understanding of how evidence behaves in the real world. It also requires restraint, as conclusions must match the quality of the samples.
The roots of the field stretch back two centuries to early efforts to quantify crime and reform punishment. In 1764, Cesare Beccaria argued that penalties should be public, prompt, necessary, minimal under the circumstances, and fixed by law, with severity tied to the harm done rather than intent. Jeremy Bentham echoed the idea that certain and proportionate punishment deters future offending. Statistical tracking in the nineteenth century and later legal codification gave researchers common baselines and laid the groundwork for contemporary analysis.
Work in the twentieth century shifted attention to social and economic conditions. In 1962, the American Law Institute completed the Model Penal Code after ten years of drafting. It influenced state reforms and federal proposals. Later theories emphasized how people learn offending in small groups and how ties to family, school, and work support self-control. Today criminology draws on sociology to study inequality and institutions, on psychology and psychiatry to study motives and risk, on anthropology for identification and behavior patterns, and on criminal law to define procedures and limits. The mix keeps research grounded in both people and rules, and it keeps labs and courts aligned on what counts as reliable proof.
Forensic chemists analyze items arriving from scenes, then explain what tests show and what they cannot show. Most work in government laboratories tied to medical examiners or police agencies, and some work in private labs. Everyday casework includes hair, fibers, glass, paint, blood, and other trace materials. DNA analysis has expanded the biological side of the job. The job requires clear testimony, so many labs train new analysts in mock courtrooms. The work rewards patience, integrity, and methodical habits. It is supported by study in criminalistics, instrumental analysis, genetics or biochemistry for DNA, and physiology and chemistry for toxicology.
It is a core set of tools because many substances interact with light in ways that reveal identity or quantity. Atomic absorption or emission methods measure elements by how free atoms absorb or emit light. Joseph Fourier transform infrared spectroscopy finds compounds fast and non-destructively, and its micro version can study very small samples around ten micrometers without using them up. Gas chromatography with mass spectrometry first separates a mix and then tells what the parts are. It is common in environmental checks, sports drug testing, and casework. Each method answers different questions, so labs pick the one that fits the sample and the decision they have to make.
Chromatography separates an unknown mixture so you can analyze each component. High performance liquid chromatography uses high-pressure pumps to force the sample through a column and helps in residues, fibers, toxins, and explosive fragments. Thin-layer chromatography provides rapid comparisons for drugs, inks, and other similar materials when fast screening is necessary. These procedures often run in parallel with spectroscopy. They start broad and end in an exact identification. Good records keep those steps traceable for court review.
The recording and collection come first because a crime scene can make or break a case. Investigators take photos and measure the area while keeping a strict chain of custody. They pick, lift, scrape, vacuum, comb, or clip small traces with tweezers, tape lifts, and spatulas. What finally survives depends on the environment, because swamps may contaminate samples and crowds can scatter evidence beyond the obvious area. In general, the temperature determines decomposition, which affects time-since-death estimates. Items then fall into physical, documentary, demonstrative, and testimonial categories that follow different rules.
Once in the lab, fingerprints can link scenes or place a person at a location, although surface type and print freshness matter. Latent prints are usually developed with powders that stick to skin oils. This makes them visible for imaging and comparison. Bloodstain patterns may show positions, movements, and the likely class of weapon. DNA, since it is unique to each person except identical twins, has strong power to include or exclude suspects. Analysts test collection methods to avoid contamination, then compare the profiles to references or databases. Each step is reviewed so the result can be defended as fair and repeatable.
Autopsies answer when, how, and where a person died by reading injuries and physiology together. Clean slices can suggest a smooth blade, and tooth-like edges can suggest a saw. Strangulation, drowning, poisoning, or falls leave patterns in organs and bones that guide the conclusion. Age and health also shape wound appearance and healing, and that matters for timing. These findings help match scene evidence with medical facts, so that the full picture is not guessed but shown.
Questioning aims for reliable accounts with protection of rights. It is accompanied by awareness of stress and by not jumping to conclusions about deception. Statements are checked against the known facts. Gaze and avoidance during key details are noted, and subtle changes in a story are elicited under light pressure. The aim is to test the claims, not to force them. The reports of the witnesses are combined with the science from the lab. Cases are closed when all evidence, interviews, and law come together in the courtroom. The sentencing varies depending on the nature of the crime and the extent of the damage. Mitigating factors include age and grave mental disorders that reduce the sentence. Certain and clear rules make people think twice. For deterrence, certainty and clarity are very important.
Two famous cases show how strong an investigation can be and where it stops. In the late nineteen sixties, in Northern California, the Zodiac killer sent taunting letters and secret codes to newspapers and the San Francisco police. He claimed more victims than the five confirmed deaths and two injuries. One code was solved in 2020, but others are still unsolved. In 1888, in London, a series of murders in Whitechapel targeted women who engaged in sex work. In several cases, the killer inflicted severe wounds, mostly to the throat and the abdomen. Some letters were allegedly sent to newspapers to spread the name Jack the Ripper. The Dear Boss letter was probably a hoax. The From Hell note came with a piece of human tissue. The canonical five victims are usually named as Mary Ann Nichols, Annie Chapman, Elizabeth Stride, Catherine Eddowes, and Mary Jane Kelly.