How DNA is collected

Discover the various sources of DNA evidence and the methods investigators use to collect it. From visible biological samples to microscopic traces, learn how crucial genetic information is gathered at a crime scene.

Blood 

Blood is one of the most common and useful sources of DNA evidence found at crime scenes. Blood contains white blood cells, which hold a person's DNA. Investigators may find blood on clothing, weapons, floors, walls, or other surfaces connected to a crime. Even dried blood that has been present for years can sometimes be analyzed using modern forensic techniques. Crime scene investigators carefully collect blood samples using sterile swabs and preserve them in special containers to prevent contamination. Blood evidence can help identify suspects, place individuals at crime scenes, and provide valuable information about how a crime occurred.

Saliva 

Saliva is another important source of DNA evidence. It can be found on cigarette butts, drinking cups, water bottles, food items, envelopes, stamps, chewing gum, and even bite marks. Saliva contains cells from the inside of the mouth that provide a rich source of DNA. Police often collect saliva samples from suspects by using a cotton swab to gather cells from inside the cheek. Because saliva is easy to collect and contains a large amount of genetic material, it has become one of the most frequently used sources of DNA in forensic investigations.

Skin Cells (touch DNA)

Every person sheds thousands of skin cells each day. When someone touches an object, they leave behind tiny traces of skin cells known as touch DNA. Investigators can collect touch DNA from objects such as door handles, steering wheels, cell phones, weapons, and clothing. Even though these cells are invisible to the naked eye, they often contain enough DNA to create a profile. Touch DNA has become increasingly important because it allows investigators to gather evidence even when no blood, saliva, or other obvious biological material is present.

Semen And Other Biological Evidence

Semen and other bodily fluids can provide extremely important DNA evidence in criminal investigations. These forms of evidence are particularly valuable in sexual assault cases because they can directly connect an offender to a victim. Scientists carefully analyze biological samples and compare the DNA to known profiles from suspects or DNA databases. Other bodily fluids, such as sweat and urine, may also contain DNA that can assist investigators. The ability to obtain DNA from various biological sources has significantly improved the accuracy of criminal investigations.

Hair With The Root Attached

Hair can provide valuable DNA evidence when the root remains attached. The root contains living cells that contain a person's DNA. Hair may be found on clothing, furniture, bedding, or at crime scenes where physical contact has occurred. Although hair without the root contains limited genetic information, advances in forensic science have allowed scientists to obtain useful DNA evidence from certain hair samples. Hair evidence can help connect suspects or victims to a particular location and provide investigators with important clues during an investigation.