Nearly every day for weeks, a white-haired man in a wheelchair, his body ravaged by diabetes and heart disease, has been escorted under heavy guard from a Texas jail cell to an interview room to speak about evil.

Day by day, the authorities say, he has recounted details of long-ago murders: faces, places, the layouts of small towns. He has described how he picked up vulnerable women from bars, nightclubs and along streets and strangled them to death in the back seat of his car.

The man, Samuel Little, 78, has confessed to more than 90 murders, investigators say, stretching back almost half a century. Mr. Little already is serving three life sentences for the murders of three Los Angeles women during the 1980s, but the authorities suspect him of killing women in at least 14 states. Investigators say they have established Mr. Little’s ties to about 30 of the murders so far, and have little reason to doubt his confessions.

[Read More: F.B.I. says Samuel Little is most prolific serial killer in U.S. History]

“By the time we are done, we anticipate that Samuel Little will be confirmed as one of the most prolific serial killers in American history,” said Bobby Bland, the district attorney of Ector County, Tex., where Mr. Little is being held after a grand jury indicted him this summer for a 1994 killing.