They are haunting drawings: black, white and Latina women, most of them youthful, with bright lips and lined eyes, staring plaintively at the viewer.

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 F.B.I. says Samuel Little, now 78 and serving consecutive life sentences for three murders in Los Angeles in the 1980s, has confessed to 93 murders 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 murders. He says he did not know many of his victims’ names — only in some cases did he know a first name or nickname — which has made identification difficult. The authorities hope that the drawings they released Tuesday, which Mr. Little made while he was in custody, will help match names to his accounts.