FRESNO (AP) — The Fresno County coroner’s office says the ex-convict who shot co-workers execution-style at a chicken processing plant and then killed himself had traces of marijuana in his system.

Coroner David Hadden said on Tuesday that a toxicology test revealed the marijuana in Lawrence Nathaniel Jones’ body. Hadden said the test doesn’t show when the 42-year-old shooter smoked the pot, or how much he had smoked.

Hadden said the tests did not find any other street drugs in Jones’ system. He said a second toxicology test will be conducted to reveal if Jones took psychiatric drugs or other substances.

Last Tuesday, in the middle of his morning shift at Valley Protein, authorities say Jones pulled a gun and shot four co-workers, killing two. Two others were wounded.

Police have not released a possible motive for the violence.