MOULTON, Alabama (AP) — A man who claims to be a contract killer for multiple drug cartels in Mexico and admitted to killing dozens of people in several U.S. states pleaded guilty Thursday to murder and was sentenced to 50 years in prison.

Jose Manuel Martinez pleaded guilty to a 2013 shooting in the southeastern state of Alabama. He is also charged in 11 alleged contract killings in California and Florida.

Investigators say that once Martinez, 52, was arrested in Arizona shortly after crossing the border from Mexico and sent to Alabama to stand trial, he claimed to be a contract killer for drug cartels who has killed dozens of people in several states. He told authorities he worked for multiple drug cartels but said he would never disclose the names or affiliations of his criminal associates.

After Martinez began confessing to multiple killings, investigators from other law enforcement agencies across the U.S. came to question him. It became clear through interviews that the slayings he spoke of had happened and he had information about them that no one else would know, authorities said.

On Thursday, according to court records show, Martinez pleaded guilty to shooting Jose Ruiz in March 2013. Investigators say Ruiz was shot to death after making a derogatory remark about Martinez's daughter.

The live-in boyfriend of Martinez's daughter was initially charged in the slaying of Ruiz, whose body was found in a field in Alabama, said defense attorney Tommy Turner.

Turner said it's unclear exactly how many people Martinez claims to have killed at this point.

"I've heard 36 or 46, but I've never asked him," he said.

While Martinez is charged in nine contract slayings in California, Turner said he will likely be prosecuted next in Florida because prosecutors there placed a judicial hold on him first.

"He was a debt collector and enforcer. The Florida cases stem from two men there who owed a huge drug debt, and he's alleged to have been sent to Florida to collect the money that was owed," Turner said.

Two men were abducted and one of their wives paid a ransom, but both were later found dead, said the attorney.

Authorities in California say he killed six people between 1980 and 2011. The victims ranged in age from 22 to 56, investigators said.

In addition to the nine murder counts, Martinez was charged in California with one count of attempted murder and the special circumstances of committing multiple murders, lying in wait and kidnapping. Four murder charges include the allegation he committed the crime for financial gain, the criminal complaint says.

The California charges would make Martinez eligible for a death sentence, if he is convicted.