The presence of blood on a crime scene can be used to elucidate the role of drugs and alcohol in an accident or crime. Using gas chromatography, forensic scientists can detect drug and alcohol concentrations in blood and urine. Gas chromatography involves vaporizing a substance in the presence of a gaseous solvent and allowing the vapor to pass through the long path of the machine. When the substance comes out of the gas and is absorbed onto a solid or liquid, its levels can be analyzed by a detector and plotted to create a chromatogram of drug levels.
DNA forensics uses the DNA portions that vary the most among humans to confirm that a suspect is actually guilty of committing a crime. Only one-tenth of a single strand of DNA differs from one person to the next, but the more DNA samples that are alike between a subject's DNA and the DNA found at a crime scene, the greater the chance that the subject was at the crime scene. In addition to confirming guilt, DNA forensics can also be used to establish paternity, to match organ donors with recipients and to prove an accused person's innocence.
Mitochondrial DNA is found in the cellular organelle called the mitochondrion, and is inherited from the mother, thus making it possible to match a subject's DNA profile to that of a family member. While nuclear DNA is usually used in forensic analysis, and is generally sufficient to establish a DNA match, in cases with limited fragments of material or deteriorated samples, mitochondrial testing may be the only option. Mitochondrial DNA can be used to establish matches in crimes that happened years ago.
Firearms analysis is the process of analyzing gunpowder and other weapons residue at a crime scene to determine whether they came from a particular firearm. Investigators must look on and in walls, floors, mattresses, ceilings and trees to find bullets, cartridges, and gunpowder residue. Then, they must document it in detail and attempt to trace it back to its class or type of firearm. Marks on a bullet, for instance, could be unique to a particular kind of firearm.