From US News:

Investigators have confirmed that Martinez is responsible for a 2006 double-homicide in Marion County, Fla., a March homicide in Lawrence County, Ala., and at least 10 other killings in California, according to sheriff’s officials.

Martinez, a U.S. citizen, told investigators that he committed those murders and more than a dozen others as an enforcer for multiple Mexican drug lords, according to Lawrence County Sheriff’s Capt. Tim McWhorter.