The women were etched in chalk pastel by the man who says he killed them, in a spree he says began in 1970 and continued for decades. If verified, that would make him among the most prolific serial killers in American history.

The FBI says Samuel Little, now 78 and serving consecutive life sentences for three murders in Los Angeles in the 1980s, has confessed to 93 across the country. He targeted marginalized women, including prostitutes and addicts, whose deaths sometimes went uninvestigated, the agency said.

Although investigators believe his confessions, they have so far matched only half to unsolved . He says he did not know many of his victim’s names — only in some cases did he know a first name or nickname — which has made identification difficult. Authorities hope the drawings they released Tuesday, which Little made while he was in custody, will help match names to his accounts.

The agency is hoping “that someone — a family member, former neighbor, friend — might recognize the victim and provide that crucial clue in helping authorities make an identification,” an agency spokeswoman, Shayne Buchwald, said in a statement.

She added that Little’s recollections and drawings have been strikingly accurate; two of his drawings have already helped investigators match his accounts to cold cases. The FBI is asking anyone with relevant information to contact the Violent Criminal Apprehension Program, or ViCAP, by calling 1-800-634-4097.

Starting in the 1960s, Little was arrested nearly 100 times in numerous states for crimes including armed robbery, rape and kidnapping. But he served fewer than 10 years in prison for those crimes.

He was linked to the Los Angeles murders in 2012 from a hit in a national DNA database. Investigators found him in Kentucky and returned him to California, where he was convicted and imprisoned. He has remained there except for a stint in Texas, where he was convicted of murder in a 1994 killing and given a concurrent sentence of life in prison.

Little, who now uses a wheelchair because of diabetes and heart disease, spent many hours detailing his crimes to investigators. He described in detail how he picked up women — whom he called “his babies” — in bars or on the street, then strangled them in his car.

In a jailhouse interview with Jillian Lauren of New York magazine, Little said he had evaded capture by preying on those whose deaths would not garner widespread public attention.

“I never killed no senators or governors or fancy New York journalists — nothing like that,” he told Lauren. “I killed you, it’d be all over the news the next day. I stayed in the ghettos.”

Angela Williamson, a senior policy adviser on forensics at the Department of Justice, noted that without Little’s confessions, investigators might never have known he had committed so many crimes. Most of the time, there was no physical evidence.

“We just want to get these girls their names back,” she said. “We want to give answers to their families or friends who are wondering what happened to them and close the cases and get some kind of resolution.”

This article originally appeared in The New York Times.