A suspected contract killer charged for carrying out nine murders in central California claimed to investigators that he had killed 40 people in a career spanning decades, a prosecutor said Wednesday.

Jose Manuel Martinez, 51, confessed that he carried out the killings while working as an enforcer for a drug cartel, Errek Jett, the district attorney in Lawrence County, Ala., where Martinez will be tried for a homicide, reportedly said. Anthony Fultz, an assistant district attorney in California's Tulare County, who filed charges against Martinez, said that he targeted victims in Tulare, Kern and Santa Barbara counties between 1980 and 2011.

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

Martinez is being held in Alabama, awaiting trial for a 2013 slaying, and Fultz said he is also wanted in Florida on suspicion of two killings in 2006. If convicted, his California charges would lead to a death sentence.

Defense attorney Thomas Turner, who represents Martinez in the case, said, according to Associated Press, that his client is innocent and doesn’t seem to be a hardened killer.

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

In addition to the nine murder counts, Martinez was also charged in California with one count of attempted murder. The criminal complaint against him reportedly states that four of the murders were done for financial gain.

According to the California Department of Corrections and Rehabilitation, Martinez had spent a brief time in state prison following a 2007 conviction on drug charges.

Loreta Fernandez, Martinez's mother, told the Los Angeles Times on Wednesday that she was completely shaken by the news of her son's alleged crimes, adding that she does not believe that her son committed the murders. 

"This is hard for me - really hard," Fernandez said. "I'm still shaking. I'm not in a condition to deal with this." She added that the last time she saw her son was in June 2013, when he was arrested while crossing the Mexican border after a warrant was issued for his arrest in Alabama.