Since time immemorial, people have been killed by people they know. The statistic for it is very high, something like 97% of all murder victims are acquainted with their murderer. It might even be higher. This is why when someone is murdered police talk to family, friends, and even acquaintances first and foremost.
There are only two types of killings that don’t fall into this; serial killings and contract killings. Even with drive-by gang related shootings, there is an acquaintanceship between killer and victim.
Even when there is a known serial killer on the loose, a stranger killing is still rarely anyone’s first thought. And unless there’s a signature, it can be difficult to connect serial kills. It’s about more than MO. It’s about more than details not released to the public. Especially, as we move away from the era when everything we knew about serial killers came from the lips of Ted Bundy.
We now know that modus operandi isn’t as constant as we once believed. As a matter of fact, serial killers often change their MO and their signatures. Of those that didn’t, we have Zodiac, BTK, and Richard Ramirez (the Night Stalker). But this was done for a reason. These were all police taunters. They wanted the police to know which kills were theirs and we could be wrong about Zodiac.
Zodiac claimed a higher body count than the police and FBI attributed to him. Catching killers like BTK have shown us a great deal we didn’t know about serial killers and estimates have been revised for Zodiac in the last two decades. Because it is possible that Zodiac was killing in multiple locations, using multiple modus operandi (this includes weapons and manner of death), and it is quite likely he didn’t sign every kill, like we originally thought.
Oddly, serial killer signatures aren’t much different than Nom de Plumes, pen names for authors. I know a half dozen authors who have multiple pen names. Each name is for a specific genre. When you think of it that way, it seems plausible that a serial killer would have multiple signatures, one for each type of killing. Sticking with Zodiac as our example, Zodiac did not sexually assault any of his victims and he shot them. That was what was looked for in the Zodiac killings, along with letters to the press and his infamous crosshairs marking of the circle with the cross through it.
If Zodiac wanted to rape and kill, he could have. If he didn’t want it associated with himself, well that’s easy enough. Stab the victim or strangle them. Don’t send a letter to the press. And don’t carve the crosshairs anywhere.
And suddenly, viola, you have Jane Doe killed by an unknown person, but even though Zodiac is killing couples in this area of California, she can’t possibly be a victim of Zodiac, because Zodiac doesn’t rape them, he doesn’t strangle them, he’s attacked only multiple victims such as couples, and he really likes to read about himself in the press and he hasn’t claimed responsibility.
Another lesson learned from serial killers of the 1990s and 2000s. Gary Ridgway (Green River Killer) and Dennis Rader (BTK), both changed how they killed on different occasions. Ridgway was known to strangle his victims. But when a hitchhiker turned up near the Green River dump site, beaten to death, she wasn’t immediately linked to the other Green River killings, because the Green River Killer strangled his victims and they were almost all known prostitutes. After Ridgway was caught, he confessed to killing the hitchhiker and he had more details than could have been gleaned from news accounts of it. Dennis Rader once taunted police by sending in the driver’s license of a woman who had been murdered, but it hadn’t been attributed to BTK. The murder had been considered too different from BTK’s other kills.
This flexibility to change MO and signature, was once believed to be impossible. It was once believed that a serial killer had to do these things in this exact manner, as if it were some kind of compulsion. Understanding that it isn’t, has changed how we look at serial killers and their victims. It has also resulted in our realization that some serial killers may have been much more successful than we thought. Applying it historically, it makes us wonder, isn’t it reasonable to think that perhaps Jack the Ripper didn’t stop killing in Whitechapel? Maybe he got tired of the gruesome gory kills. Maybe he refined how he killed. Whitechapel was an area where murder was fairly common. If he decided to stop butchering his victims, it is very likely he continued to kill and they just weren’t “Ripperesque” enough to be attributed to him. The same could be true of Zodiac and several others. Which makes that 37 Zodiac chillingly scrawled on one of his notes, seem plausible or perhaps the word is probable.