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Getting the Big Picture: Forensics in Action

You witness a burglar sneaking away from a store late at night. You call the police, and when they arrive, you identify the thief as someone you know. That person is arrested. However, fingerprints from the store's broken window, cracked safe, and tools used to open the safe don't match up with those of the person you've fingered. Instead, they match the fingerprints of a known safecracker. What do you think police, prosecutors, and more important, the jury are going to believe? After all, it was dark and raining, you were 100 feet away, you caught only a glimpse of the thief, and you'd just left a bar where you'd had a couple of drinks with friends. The fingerprints, on the other hand, match those of a known thief in each and every detail, meaning they came from him and only him. Which bit of evidence, the fingerprints or your eyewitness account, is more reliable?

This scenario represents what forensics does or at least attempts to do. Each and every forensic technique is designed to either identify a perpetrator or connect him or her to the crime.

Starting out small: Basic forensic services

Properly identifying, collecting, documenting, and storing evidence are at the heart of the forensic services offered by virtually all law enforcement agencies, from village cop to major metropolitan police department. They need the basic services in the list that follows to be able to investigate and solve crimes and to convict the criminals who commit them:

  • Evidence collection unit: This crime-scene investigation unit collects and preserves evidence from the crime scene and transports it to the lab. Regardless of whether they're individual police officers or highly trained professionals, members of this unit expose and lift latent fingerprints, collect hair and fibers, and gather any other articles of evidence at the scene.
  • Photography unit: The photography unit takes pictures of the crime scene, all evidence, and the body (whenever one is present). These photos are crucial, serving as blueprints for crime-scene reconstruction and an excellent format for presenting evidence in the courtroom.
  • Evidence storage: A secure place for storing and preserving the evidence is essential. Evidence is usually stored in a locked room with restricted access that is housed at your local police station or sheriff's department. Evidentiary materials are kept in storage for years or even decades, and the chain of custody must remain unbroken throughout that time, or the evidence can be compromised, losing its value.

Finding out about physical forensic science

Tracking down trace evidence, checking the ballistics of bullets fired from a gun, examining the penmanship of a signature on an important document, and checking out the swirling ridges of fingerprints under a microscope all are part of the physical side of forensic science.

  • Trace evidence: Any small item of evidence — hair, fiber, paint, glass, or soil, for example — that places the suspect at the scene of the crime or in direct contact with the victim is considered trace evidence. Matching glass fragments found on the victim of a hit-and-run motor-vehicle accident to glass from the broken headlamp of the suspect's car is a prime example.
  • Firearms identification: Firearms identification deals with the examination of weapons and the projectiles they fire, including ammunition, fired bullets, shell casings, and shotgun shells. Firearms experts use a microscope and various types of chemical analysis to identify the type of weapon used to commit a crime and match any bullets fired from that weapon or shell casings to a suspect weapon.
  • Document examination: Whenever an important written document's age or authenticity is in doubt, a document examiner uses handwriting analysis to match handwriting samples to questioned documents or signatures. Document examination also may include analyzing the physical and chemical properties of papers and inks or exposing indented writing (the impressions made on the page beneath one that was written on). Typewritten or photocopied documents that may have been altered also fall under the document examiner's area of expertise.
  • Fingerprint examination: Fingerprint examiners match prints to the fingers, palms, or soles of the people who left them at the crime scene. A print found at a crime scene can be compared with another taken from a database or from a suspect, victim, or bystander.

Delving into biological forensic science

Forensics deals not only with physical evidence but also with biological evidence, which may take the form of a corpse, skeletal remains, drugs and poisons, teeth, bite marks, insects, and plant materials, to name a few. It also includes analysis of the criminal mind. Biological evidence is often what makes or breaks a case.

For example, an autopsy (postmortem examination of the body) may reveal the nature and cause of any injuries, the presence of any poisons, and ultimately why and how the victim died. These findings alone may lead to the perpetrator. Blood and DNA analysis can positively identify a suspect and link him or her to a crime. DNA and dental pattern records can be used to identify an unidentified corpse, and plant and insect evidence can reveal the time of death and link a suspect to the crime scene.

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