The FBI searched two produce companies Wednesday for evidence of a crime in the nationwide E. coli outbreak that killed one person and sickened at least 192 others.

Agents from the FBI and the Food and Drug Administration used warrants to search a Natural Selection Foods LLC plant in San Juan Bautista and a Growers Express plant in Salinas to determine whether they followed food safety procedures, according to the Associated Press.

Natural Selection, which packages spinach sold under 34 brand names and supplies spinach to other food processors, was implicated in the E. coli outbreak after 11 bags of Dole brand baby spinach tested positive for the same bacteria strain found in people who fell ill after eating the leafy greens.

Growers Express grows and packs produce, including Farm Day packaged spinach. Until Wednesday, the company had not been named in the investigation of how the tainted spinach ended up in bags and on store shelves.

Federal officials do not think anyone at the plants deliberately contaminated spinach with the virulent bacteria and said the searches do not mean there is an ongoing or new threat to public health.

Companies can be convicted if they are shown to have been negligent in preventing tainted foods from entering the market, even if they were unaware of the contamination.