DNA evidence

1. DNA evidence BCT 2005-6 DNA evidence

2. Blood • At one time, blood at a crime scene was significant to investigators for its presence alone — bloodstains and spatters often tell their own story of events. But today scientists can perform further tests, including blood typing and DNA analysis, that can help identify the victim or offender. Pictured here is a color-enhanced image of blood cells and platelets, magnified over 5,200 times by a scanning electron microscope. DNA evidence

3. Investigators can extract DNA from saliva left behind on items — such as cigarettes, envelopes or drinking straws — at the crime scene to help identify their killer or victim. One suspect was connected to the World Trade Center bombing, for example, after authorities matched his DNA with that from saliva on an envelope delivered by one of the conspirators. This saliva has been magnified 40 times. Saliva DNA evidence

4. In cases of rape and other sexual crimes, the seminal fluid left by the attacker can provide important evidence. Since sperm remains alive for only a short period of time, its condition can indicate the time of the attack; such samples can also provide information on blood type and now identity, through DNA. Pictured here is a color-enhanced image of sperm, magnified over 3,000 times by a scanning electron microscope. Sperm DNA evidence

5. While their utility is still under debate, fingernails, like fingerprints, are thought to be unique and thus useful in linking suspects to crime scenes. This is because the underside of fingernails and toenails have grooves, called striations, that form a pattern unique to each finger or toe; nails from one individual match up to their owner much like bullets fired from the same gun. Fingernail evidence has been used in several U.S. cases since the mid-1970s. Pictured here is a section of fingernail magnified over 300 times by a scanning electron microscope. Fingernail DNA evidence

6. Forensic scientists can analyze the DNA found in the cells of a single hair root to identify their killer or victim. Investigators often find hairs with roots attached at crime scenes, indicating a struggle took place. Pictured here is a color-enhanced image of a hair root, magnified over 90 times by a scanning electron microscope. Hair root DNA evidence

7. DNA can sometimes be obtained from skin cells that an attacker unwittingly leaves beneath the fingernails of a victim during a fight. In one case, police found a victim with hair clutched in her hand and skin under her nails; investigators were able to use this evidence to link her husband to the crime. Pictured here is a color-enhanced image of a healthy skin surface, magnified nearly 1,000 times by a scanning electron microscope. Human skin DNA evidence

8. Hair: which is animal? DNA evidence

9. The random assortment of trace materials — such as the hair, fibers, insect scales, pollen and plant remains shown here — makes each building's dust unique. This color-enhanced image was magnified over 115 times by a scanning electron microscope. Household dust DNA evidence

10. Just take a look at the lint collected in your dryer; our clothes are constantly shedding, leaving behind a telltale trail wherever we go. Here, a shirt's natural cotton fibers appear green; its man-made polyester fibers appear yellow. This image was magnified over 600 times by a scanning electron microscope. Shirt fibers DNA evidence

11. Dust mites join an assortment of fibers in this sample of dust. This color-enhanced image was magnified over 400 times by a scanning electron microscope. Dust mites DNA evidence

12. Pollen — which can be breathed in, consumed or discovered on clothing — can have a lot to say to a forensic investigator. Tracing a pollen sample to its species of origin can indicate in what season a person died and what kinds of plants grew nearby, for example. This picture contains three types of pollen: daisy (prickly), cherry (oblong) and hornbeam (round). It was color-enhanced and magnified over 1,100 times by a scanning electron microscope. Pollen DNA evidence