As San Francisco Chronicle Staff Writers Stacy Finz and Marisa Lagos report, the investigation into the source of a deadly E. coli outbreak that has sickened nearly 200 people moved into the criminal realm for the first time today, as federal search warrants were executed at two Salinas Valley produce companies.

Investigators for the FBI and the U.S. Food and Drug Administration went into Natural Selection Foods LLC in San Juan Bautista and into the Green Giant Fresh by Growers Express plant in Salinas.

The agents are looking into possible violations of federal environmental laws, authorities said.

At Natural Selection Foods, investigators were hunting for quality assurance documents and other paperwork, sources said. The company has already been tied by the FDC to the E. coli outbreak in bagged Spinach that has killed one person and sickened 191 others in North America.