Wow. The evil is overwhelming.

ST. PETERSBURG, Fla. (AP) — The inmate who claims to have killed more than 90 women across the country is now considered to be the most prolific serial killer in U.S. history, the Federal Bureau of Investigation said.

Samuel Little, who has been behind bars since 2012, told investigators last year that he was responsible for about 90 killings nationwide between 1970 and 2005. In a news release on Sunday, the FBI announced that federal crime analysts believe all of his confessions are credible, and officials have been able to verify 50 confessions so far.

Investigators also provided new information and details about five cases in Florida, Arkansas, Kentucky, Nevada and Louisiana.

The 79-year-old Little is serving multiple life sentences in California. He says he strangled his 93 victims, nearly all of them women.

Some of his victims were on the margins of society. Many were originally deemed overdoses, or attributed to accidental or undetermined causes. Some bodies were never found.