In addition to his prison cell conversations with law enforcement officials, Mr. Little has drawn dozens of detailed portraits of his victims, sketching them in chalk pastels. Over 45 years, he targeted marginalized women, including prostitutes and drug users, the authorities say. Most of them were African-American. He often knew only their first names, or nicknames. The F.B.I. noted that many of the deaths of Mr. Little’s victims had originally been ruled as overdoses or from accidental or unknown causes. In other cases, the women went missing and their bodies were never found, but their cases drew little attention.

While Mr. Little has offered many details, investigators fear that his memory is becoming not entirely reliable. He is often fuzzy on the year a killing took place. That can make matching his version of events to local police records challenging — and help from the public even more essential, according to investigators.

Among the five new sketches released to the public, one depicts a transgender woman named Marianne that Mr. Little met in Miami in 1971 or 1972. Mr. Little said she was 18 or 19 years old and they met at a bar. He offered her a ride home in his gold Pontiac LeMans, then drove to what might have been a sugar cane field near Highway 27, where he killed her, according to the authorities.

In a series of videotaped interviews with Mr. Little from a prison cell that were released by the F.B.I. this week, Mr. Little became visibly excited as he discussed the killings. Asked by a detective about a woman he said he killed in North Little Rock, Ark., in 1994, Mr. Little responded: “Oh, man, I loved her. I forget her name. Oh, yeah. I think it was Ruth.”