LA Forensics: The Signature Murders
Understanding a signature involves behavioral analysis: specifically, examining what a perpetrator does at a scene that's unnecessary to accomplish his or her goal and that appears to be performed to meet some inner personal need.
Dr. Robert D. Keppel in Washington State was among the first to describe and discuss signature analysis. He was deeply involved in the Ted Bundy and Green River Killer investigations, had interviewed Bundy about serial killers, and wrote the definitive book, Signature Killers. To Keppel's mind, the issue is control. These men are life's losers, who feel powerless and are seeking power through murder. The need to feel better about themselves generates a compulsion to find and control victims in a specific way and they act out the same compulsion repeatedly.
The killer will either use the murder scenario to build sexual tension and ejaculate at the scene, or will delay release and substitute certain rituals, such as posing the victim, to indicate sexual subservience. "Signature killers are sexual offenders at the far end of the violence continuum," Keppel says, "who leave their psychological imprints at crime scenes to gratify their sexual needs." Since what they do sets their murders or rapes apart, they may provide patterns that indicate how best to hunt them down. Even when a clever killer tries to throw off the investigation, certain repetitions give him away. As Keppel explains, "It lies within the very nature of the killer that his signature will be recreated in each and every murder he commits."
These murders involve progression and escalation. Either they become more intense, with bolder expression of the ritual, or they are done increasingly more often. The way the killer selects, approaches, kills and poses a victim reveals his "psychological calling card." Those who can read signatures have a higher success rate in stopping these criminals.
Even when the MO — the way a crime was committed —changes from one incident to the next the signature nevertheless links the crimes and reveals the killers' essential vulnerability. They're compelled to leave their imprints: Some always choose a victim with the same hairstyle; some always abuse the corpse after death; some always ejaculate next to the body. At least one liked to leave a coiled leather belt.
Whatever the compulsion, it will be—must be—repeated. In essence, signature reveals intent, and the intent is always the same, because it never gets fully satisfied.