FRESNO -- A suspected contract killer charged in Central California with murdering nine people confessed to investigators that he carried out up to 40 slayings in a career spanning decades, a prosecutor said Wednesday.

Errek Jett, the district attorney in Lawrence County, Alabama, said that Jose Manuel Martinez, 51, told investigators he carried out the crimes working as an enforcer for a drug cartel. Jett said they believe Martinez because of the details he gave investigators.

Martinez was arrested last year shortly after crossing the border from Mexico into Arizona and sent to Alabama, where he awaits trial on one murder charge. Once word got out, a steady stream of investigators from across the country came to question Martinez, Jett said.

Defense attorney Thomas Turner, who represents Martinez in that lone case, said his client is eager to start trial in Alabama, so he can return to California. Turner said Martinez maintains his innocence of the charge there and doesn't seem to be a hardened killer.

"I've found him to be polite and a likable individual," Turner said. "He has a good personality as far as talking with him."

Prosecutors in California say otherwise.

Martinez targeted victims in Tulare, Kern and Santa Barbara counties between 1980 and 2011, Tulare County Assistant District Attorney Anthony Fultz said. He was charged with the nine slayings on Tuesday.

Martinez has lived on and off in Richgrove, a small farming community in Central California about 40 miles north of Bakersfield. He's now being held in Alabama, awaiting trial in a 2013 slaying, and Fultz said he's also wanted in Florida on suspicion of two killings there in 2006.

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

Fultz said he is confident Martinez committed at least the nine killings he's charged with, but he has heard figures as high as 30 from across the nation.

"We're actually not sure what the full scope is," Fultz said. "It will depend upon what the investigation shows."

Fultz declined to comment on any connection Martinez may have had with drug cartels, saying he did not want to damage the case at this early stage. Fultz said that too will remain under investigation.

Acting Tulare County Sheriff Mike Boudreaux said his deputies came in contact with Martinez investigating a rash of home invasion robberies in late 2012 and early 2013. Martinez was at a home searched and questioned by Sgt. Christal Derington, but not considered a suspect.

Investigators have released some details of their case, saying six of the victims were killed in Tulare County, two in Kern and one in Santa Barbara. They ranged in age from 22 to 56, investigators said.

One man was shot dead in 1980 driving to work in the morning, while two men were shot in 1982 working on a ranch, one surviving.