In criminal investigations, blood used as criminal evidence may be referred to as blood evidence. For example, human blood found on a knife blade could simply mean a person has cut himself while chopping vegetables. It could, on the other hand, mean that the knife was used to stab someone. Blood evidence may be used not only in determining whether a crime has been committed, but also in identifying the victim and perpetrator of the crime.
In some cases, blood evidence may be used to determine whether a crime has been committed. For example, if a person is reported as missing, investigators may examine the home of a person suspected of harming him. The investigators may find drops of blood on the floor or other surfaces and collect and analyze them. Analysis of this blood evidence could reveal that the blood is human and not the suspect’s or that it is animal blood. If the blood is human, however, investigators may analyze it to determine whether it belongs to the missing person.
Sometimes blood evidence can also provide important information about the perpetrator of a crime. If, for example, there was a murder that involved a violent struggle, there may be lots of the victim’s blood at the crime scene. If the criminal who committed the murder, however, was also injured during the struggle, investigators may find his blood at the crime scene as well. This blood evidence may help investigators determine who the murder suspect is and may even help prosecutors prove their case in court.
In many cases, blood evidence patterns may help investigators solve crimes. For example, an investigator may examine blood splatters and drips to figure out the type of weapon that may have been used and how the crime was committed. In fact, a crime investigator may even use bloody footprints and fingerprints to help him retrace a criminal's steps.
In some cases, a criminal may attempt to hide his crime by wiping away blood that could be used as evidence. Cleaning up after committing a crime may not be a foolproof method of escaping justice, however. Investigators may use black lights and chemicals to find blood evidence a criminal has tried to erase. For example, investigators may use a substance called luminol and black lights to find traces of blood. If a trace of blood is present on the surfaces in question, it will typically glow when black lights are used.