 The Forensic Biology and DNA Unit occupies the entire second floor of the Denver Police Crime Laboratory. The Forensic Biology Unit examines evidence recovered from crime scenes for potential biological matter. They identify biological fluids, then take swabs or cuttings from the evidence and process them for analysis. Cases that test positive in the Forensic Biology Unit go on to Forensic DNA Analysis. The goal of the DNA Unit is to develop DNA profiles from items of evidence and compare them to known DNA profiles from crime investigations. Evidence is examined from many types of cases including homicides, sexual assaults, robberies, aggravated assaults, kidnapping, and property crimes like burglaries and theft from a motor vehicle. Cold cases are also examined including homicides and sexual assaults dating back to the 1960s. Work in the Forensic Biology Unit begins with a visual examination of evidence for staining. Biologists take samples of potential stains to test for the presence of blood, semen, saliva, or cellular material. Hares can also be tested if they contain roots suitable for DNA analysis. Stains not visible to the naked eye can be located with an alternative light source. Some body fluids fluoresce under this blue light, making it a useful tool for finding stains that aren't visible using natural light. Any biological evidence obtained is stored in a walk-in freezer until it's ready for DNA analysis. The DNA analysis process uses a variety of manual and cutting-edge robotic methods to analyze samples and develop DNA profiles. Every DNA sample goes through a four-step process. The first is a DNA extraction, which is done to purify the DNA in a sample. After extraction, samples are passed through a secure chamber from the pre-amplification to the post-amplification laboratory. The next step is DNA quantitation, which determines how much DNA is present in each sample. That's followed by an amplification step, where the DNA is copied millions of times. Finally, the DNA is detected on an instrument called a genetic analyzer. This machine assembles the finished DNA profile, which analysts use to determine if biologic evidence from a crime scene matches the known DNA profile of a victim or suspect. DNA cases that are submitted without a known suspect can be searched in the combined DNA index system, or CODIS database. This is the largest DNA catalog in the world, with over 14 million profiles. CODIS is used by law enforcement agencies in the United States to help solve unsolved cases.