A 78-year-old prisoner who says he killed about 90 people over nearly four decades as he moved around the country pleaded guilty to murder Thursday in the 1994 strangulation of a Texas woman.

Samuel Little entered his plea in the West Texas city of Odessa, where the body of Denise Christie Brothers was discovered in a vacant lot about a month after she disappeared. He received another life prison term, Ector County District Attorney Bobby Bland said in a statement.

"Due to the efforts of law enforcement agencies from around the country, dozens of victims' families now have answers," Bland said. "Although this is a conviction in Ector County, Texas, I hope it will serve as justice for all those atrocious murders committed across this nation in this unprecedented era of terror and mayhem caused by Samuel Little."

Little was convicted in 2014 of killing three Los Angeles-area women in separate attacks in the late 1980s and was serving life sentences when authorities say he confessed this year to killing dozens more people in 20 states since 1970.

Those confessions, which often included a level of detail and recall that authorities say was uncanny, spurred investigators from Florida to California to review old murder cases. An FBI spokesman said thus far, investigators have concluded that Little was the killer in 36 cases, including the killing of Brothers and the three in the Los Angeles-area that landed him in prison. But Bland said in his statement more than 40 cases have been confirmed. He later explained that he received that number from Texas Rangers, an elite investigative agency that has relayed details of Little's confessions to law officers in other states. Little explained the killings in a series of conversations with Ranger James Holland.

Most recently, police in Tennessee linked Little to the death of Martha Cunningham, a Knoxville woman whose body was found in a wooded area by a road in 1975. Even though Cunningham was bruised and nude from the waist down when her body was found, detectives attributed her death to natural causes, according to the Knoxville News Sentinel.

With at least three-dozen confirmed deaths, Little is already among the most prolific known serial killers in American history. Gary Ridgway, the so-called Green River killer who is serving life in prison, pleaded guilty to killing 49 women and girls, making him the deadliest serial killer in terms of confirmed kills, though he has said he likely killed more than 71 people. Ted Bundy confessed to 30 homicides from about 1974 to 1978 and John Wayne Gacy killed at least 33 young men and boys in the 1970s. Both of them were executed.

Little, who is in poor health and relies on a wheelchair, offered his confessions as a bargaining chip to be moved from the Los Angeles County prison where he was being held, the FBI said last month. But Bland said Thursday that Little will return to California to serve his life term.

Little, who also went by the name Samuel McDowell, targeted vulnerable women who were often involved in prostitution and addicted to drugs, authorities have said. Once a competitive boxer, he usually stunned or knocked out his victims with powerful punches before he strangled them while masturbating.

"With no stab marks or bullet wounds, many of these deaths were not classified as homicides but attributed to drug overdoses, accidents, or natural causes," the FBI said.