Thirty-two years after his last murder, the Golden State Killer may be behind bars, according to California authorities.
Local and federal law enforcement arrested Joseph James DeAngelo Jr. on Tuesday, saying that DNA evidence shows him to be responsible for 10 murders and at least 46 rapes from the 1970s to 1986. According to the Los Angeles Times, DeAngelo, now 72, has been married since 1973. He and his wife have three children.
DeAngelo's apparent quiet suburban life may not be unusual for serial killers, experts say. There is no foolproof estimate for how many such criminals are living in communities, uncaptured, but Thomas Hargrove, the founder of the Murder Accountability Project, argued that there are as many as 2,000 serial killers at large — and that financial woes affecting city services could be making the problem worse. [Mistaken Identity? 10 Contested Death Penalty Cases]
"We are becoming less likely to solve murders," Hargrove told Live Science.
The FBI defines a "serial killer" as someone who murders two or more victims, with a cooling-off period between crimes.
Hargrove, a retired investigative journalist, arrived at his estimate of about 2,000 at-large serial killers by asking some contacts at the FBI to calculate how many unsolved murders linked to at least one other murder through DNA were in their database, he explained to The New Yorker last year. Those officials determined that about 1,400 murders, or 2 percent of those in the database, met that classification.
However, not all murder cases involve DNA evidence, and not all cases are reported to the FBI, so that 2 percent is a low estimate, Hargrove said. Two thousand is a ballpark figure, but the numbers shouldn't be a surprise, he said.
"There are more than 220,000 unsolved murders since 1980, so when you put that in perspective, how shocking is it that there are at least 2,000 unrecognized series of homicides?" he said.
The most prolific serial killer of the modern era was probably Harold Shipman, an English doctor who may have murdered as many as 250 patients with fatal doses of painkillers. The 2,000 theoretical killers don't have to meet such a staggering standard, considering that killing a minimum of two victims in separate incidents meets the FBI definition of serial killer.
By a far more conservative method of accounting, there are about 115 serial killers dating back to the 1970s in the United States whose crimes have never been solved. That estimate comes from Kenna Quinet, a criminologist at Indiana University-Purdue University Indianapolis. It's based on linkages between cases made by journalists or law enforcement, and includes a slightly different metric than Hargrove's estimate: The killer had to have murdered at least three victims, not two.
In the same time period as Quinet's estimate for unsolved serial murders, there were roughly 625 solved serial murder cases, she told Live Science. There aren't many differences between unsolved and solved cases, geographically or in terms of factors like the type of victims, Quinet said. But her database doesn’t include cases where no one has ever made the link between murders. If a serial killer killed a person in one state and then drifted off to the next to kill two more, for example, the crimes might have never been flagged by anyone as related and thus wouldn't appear in Quinet's count.
"Somewhere in between my number and Thomas Hargrove's number is probably the right number," she said.
According to research by psychology professor Mike Aamodt at Radford University in Virginia, there were likely about 30 active serial killers operating in the United States as of 2015.
Serial killings peaked in the 1980s, Quinet said. Aamodt estimates that an average of 145 serial killers (under the two-victim minimum definition) were active in the 1980s each year, compared with an average of 54 each year between 2010 and 2015. There doesn't seem to be any single reason for serial killings' decline, Quinet said. People engage in fewer behaviors today that make them a target — hitchhiking is far rarer now than 30 years ago, for example — but the decline has largely tracked with an overall drop in the homicide rate since the early 1990s, a drop that criminologists cannot fully explain.
Why serial killers avoid capture
The biggest reason that killers of two or more people can still live free is the problem of "linkage blindness," Hargrove said. Homicide detectives are assigned single cases, and unless one happens to chat with a colleague who has a very similar case on his or her docket, those cases are unlikely to be linked, he said.
"If the murders occur at separate jurisdictions, such conversations never happen," Hargrove said.
Despite an advent of forensic DNA databases, there is still no central clearinghouse for homicide cases or serial killer cases, said retired FBI profiler Mary Ellen O'Toole, who worked on several serial killing cases during her career.The FBI collects data through the Violent Criminal Apprehension Program (ViCAP), O'Toole said, but it is not mandatory for local law enforcement to report their cases to that program. If it were, she said, it might be easier to connect homicide cases.
In the Golden State Killer case, proper storage of forensic evidence plus advances in technology seem to be the key to cracking the murders. It's possible to process very old forensic evidence with new methods, O'Toole told Live Science.
"The case itself may be cold, but forensic evidence doesn't die," she said.
Unfortunately, if technology opens new doors for solving serial murders, a lack of money may slam them shut. Insufficient funding for detectives and technicians keeps police from solving many murders, Hargrove said. According to FBI estimates, only 59 percent of homicide investigations in the U.S. have resulted in an arrest, much less a conviction. The numbers are even worse for rape (36.5 percent) and robbery (29.6 percent).
The rate for cleared homicide cases is "the lowest in the Western world," Hargrove said.
Other reasons may also explain the low rate of arrests, including a high bar for making an arrest as well as what some call an increasing no-snitch culture, especially among some minority groups who are reluctant to come forward as witnesses, according to experts interviewed by NPR.
"The problem is," Hargrove said, "everything's going the wrong way."
Original article on Live Science.
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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.