LA Forensics: The Signature Murders
Criminalists Harry Klann and Patricia Pape arrived to process the evidence. Criminalists operate on the Locard Principle of Exchange: every contact involves a transfer. In other words, people bring something to a scene and take something away with them, on their persons.
Klann and Pape first secured the outside and collected the knife. They also looked for shoeprints, clothing or items dropped as the intruder left the scene.
Inside, they decided on a search pattern in order to collect evidence in the most organized and efficient way possible. They could start near the body and work their way outward, or spiral around until they got to the body. (It's not stated which method they chose.)
There was no need to do a spatter pattern analysis, since they did not need to re-enact any complex activity, so they would concentrate on extracting DNA. They collected samples from near the victim, the furniture, items in the drawers, the hallway wall, and especially the bathroom sink. The blood in the bathroom was the intruder's and not the victim's. In addition, on the floor of the bedroom they picked up a bloodstained coupon for the department store, JC Penney. In all, they collected about 40 samples.
Historically, among the earliest ways to link a suspect to a victim via physical evidence was through the analysis of blood types, and at first that meant by isolating blood evidence according to one of the four major blood types. While not very discriminating, it was better than nothing. Blood typing could at least eliminate a suspect from having left blood at the scene if his type did not match the sample. As more research was done on blood, the analysis examined proteins and enzymes present in ratios specific to individuals.
The discipline of serology, or the analysis of serums, also made another important discovery. Around eighty percent of the members of the human race were found to be "secretors," which means that the specific types of antigens, proteins, antibodies, and enzyme characteristic of their blood can be found in other bodily fluids and tissues. By examining saliva, semen, and even teardrops, analysts can tell the blood type.
These days, thanks to a discovery in 1986, DNA technology has replaced the tests for specific enzymes and proteins. Each of the samples collected would be analyzed for its DNA profile. SID had been at the scene about four hours.
At the Garcia scene, the other piece of evidence of supreme importance was the electrical cord from the clock radio that had been wrapped around the victim's neck. This offered behavioral evidence, and could as well provide DNA from sweat on the killer's hands.
The coroner arrived and took charge of the body. It was his opinion, from various signs, that the victim had been dead for at least twenty-four hours.
As the physical evidence was processed, the detectives started to collect information about the deceased, to try to determine if he had an enemy or had crossed paths with someone who had reason to harm him. They also wanted to know when he was last seen alive.