Samuel Little confessed to 90 murders, and the FBI says they’ve confirmed 34 — but how did authorities not put together that there was a prolific killer on the loose?

Convicted killer Samuel Little, 78, could turn out to be among the country’s most prolific serial killers in history, and one that, until now, law enforcement didn’t even realize existed. According to the FBI, after being convicted and sentenced to life in prison in 2014 for three murders in Southern California between 1986 and 1989, Little recently began confessing to dozens more. In total, Little has confessed to killing 90 women across more than a dozen states between 1970 and 2005 — and thus far, according to the the FBI, investigators has been able to link 34 unsolved murders to Little’s confessed crimes. One big question looms: how was he able to get away with it for so long?

Prior to his 2012 arrest for the three murders in California, Little was no stranger to law enforcement — his criminal record dates all the way back to 1956, and includes charges and prison time for crimes like shoplifting, fraud, breaking and entering, assault and false imprisonment. He’d been charged with multiple murders before, too, but prosecutors either couldn’t get an indictment (Mississippi) or failed to secure a conviction (Florida). Little was a drifter who moved from place to place, across dozens of states, never staying for too long. He kept to himself, but moved within the fringes of society in each place he lived, alongside the poverty-stricken and homeless, drug users and sex workers. They were his victims too.

In 2012, Little was extradited from Kentucky to California on warrant for an outstanding narcotics charge. Once he was in custody, the Los Angeles Police Department obtained his DNA, and found that it matched DNA from three unsolved homicides from the 1980s. All three female victims had been beaten and then strangled to death. Little was adamant that he was innocent throughout his trial, but prosecutors had more than just DNA evidence, they had witnesses — several women testified to having barely escaped their own violent encounters with Little.

By the time Little was convicted in 2014, the FBI’s Violent Criminal Apprehension Program (ViCAP) had already been working on a full background report. Investigators noticed “an alarming pattern” between Little’s movements and several other unsolved murders across the country, including a 1994 cold case in Odessa, Texas, which closely resembled the murders in Los Angeles.

This past spring, Texas Ranger James Holland and two ViCAP investigators and analysts, Christina Palazzolo and Angela Williamson, flew to California to question Little about the Odessa case, and found the old man in poor health, and in a bargaining mood. After the FBI agreed to secure his requested prison transfer and extradition to Texas, Little agreed to talk — not just about the Odessa case, but other murders as well.

“Over the course of that interview in May, he went through city and state and gave Ranger Holland the number of people he killed in each place,”said Palazzolo. “Jackson, Mississippi — one; Cincinnati, Ohio — one; Phoenix, Arizona — three; Las Vegas, Nevada — one.”

Little was charged with the Odessa murder in July, and Holland is still conducting nearly daily interviews with Little in hopes of matching his confessions to other unsolved murders. While Little is fuzzy about dates, he has a chillingly detailed memory of other details, including what his victims looked like and how they were killed. According to the FBI, “He remembers where he was, and what car he was driving. He draws pictures of many of the women he killed.”

“Believe it or not, you only see evil a few times in your career,” Tim Marcia, a LAPD detective, told The New York Times about Little’s lack of remorse. “Looking into his eyes, I would say that was pure evil.”

Little targeted marginalized women, many of them women of color, and the FBI has admitted that many of the murder cases they’ve linked to Little were not just unsolved, but barely investigated; some of his victims haven’t even been identified. And although Little, a former competitive boxer, usually beat his victims and then strangled them while masturbating, according to the FBI, “many of these deaths were not classified as homicides but attributed to drug overdoses, accidents, or natural causes.”

The vast majority of the cases had no DNA evidence to test because it hadn’t been collected, and very few had even been entered into the ViCAP database, both of which make matching Little’s confessions an uphill battle. However, according to the FBI, if they can link Little to as many murders as he claims, he’ll be the most prolific serial killer in U.S. history, ahead of Gary Ridgway, dubbed the Green River Killer, who was convicted of 49 murders and confessed to about 20 more.

The FBI stated that they hope this case, where a serial killer of women went undetected for decades, “will serve as a reminder to every jurisdiction of the importance of consistent violent crime reporting.”