Crime scenes are known to contain many clues. The obvious would be the body or bodies, the clothes and sometimes even the murder weapon. While these are a great way to solve a case, there is another type of evidence; trace evidence. Traces are small pieces of evidence found at the crime scene. There are many types of traces, some of which include metal filings, plastic fragments, gunshot residue, glass fragments, feathers, food stains, building materials, lubricants, nail scrapings, pollen and spores, cosmetics, chemicals, paper fibers and sawdust, human traces and animal hair, plant and plant fibers, blood and other body fluids, asphalt or tar, vegetable fats and oils, dust and other airborne particles, insulators, textile fibers, soot, soil and mineral granules and explosive residues. While these are the most common items found, they are not the only ones. The Trace Evidence Unit is known to examine the widest variety of evidence types and use the widest range of analytical methods of any unit. materials are compared to known standards or samples to determine whether or not they share common characteristics. In this article I will discuss the different types of leads and how crime scene investigators use them to solve cases and convict criminals. The tracks were first discovered by Edmond Locard. Edmond Locard was born in 1877 and founded the Institute of Criminology of Lyon. He is also known for advancing the science of fingerprinting. In 1910 he was authorized to start a small forensic laboratory in the Palace of Justice which he directed until 1951. While there he worked on methods of criminal identification including poroscopy, the microscopic examination of fingerprints; analysis of body fluids, hair and skin; and graphometric or handwriting analysis. He is the man responsible for developing the theory that when two objects come into contact with each other they leave behind some sort of material matter. This theory was later called Locard's Exchange Principle. The idea is that evidence can be used to associate objects, individuals or places with each other. "A person typically loses about 100 hairs a day. These hairs may have evidentiary value in showing contact between two people. With an appropriate standard of hair, a chemist will be able to microscopically compare a... piece of paper.. . a piece of furniture that could be locked. Then he will use the small paint chips and metal as evidence and process them as that individual every piece of evidence must be examined. Believe it or not, even a victim's injuries are evidence The wound can allow investigators to compare any marks that may have been left by the weapon and therefore allows them to determine at what angle and distance and the speed at which the weapon was used I will talk about are documents. Each one has different handwriting and different characteristics that make it unique. Computers are also unique in the way they can type and print things. Examine them and establish similarities in handwriting. Computer forensic specialists can extract records and. other data from most devices. As you can see, there is no such thing as a perfect crime. You can find the smallest piece of hair, paint or anything left behind. Suspects often don't see this tiny piece of evidence and while they examined it, it was still lurking at the crime scene. A crime scene investigator is guaranteed to find this evidence, no matter how small, and use it to find, prosecute, and convict a criminal.