Stephen Sundlof, head of the Food and Drug Administration's food safety center, said the Justice Department will join FDA investigators in looking into possible criminal violations. The Peanut Corp. of America plant shipped allegedly tainted products to dozens of other food companies.
"It is an open investigation at this time," said Sundlof. "We can't really talk much about the investigation itself."
Inside the Georgia plant, FDA inspectors found roaches, mold and a leaking roof, reports CBS News correspondent Mark Strassmann.
At least a dozen times since 2007, FDA documents show plant officials knew peanut products had salmonella contamination, reports Strassmann. Instead of throwing them away, the company allegedly retested them - then shipped them into the food supply.
Georgia state inspectors are also under a microscope, adds Strassmann. One of its inspectors found violations last October, but there was no follow-up until this month.
More than 500 people have been sickened as a result of the outbreak, and at least eight may have died because of salmonella infections. More than 430 products have been pulled off the shelves in a recall that reaches to Canada and Europe.
In another development Friday, officials urged consumers to be cautious about "boutique" brands of peanut butter, which had not previously figured in the recall.
Although national brands of peanut butter are unaffected, some smaller companies may have received peanuts from the processing plant in Blakely, Ga., the FDA said.
Meanwhile, the White House pledged stricter oversight of food safety.
Press secretary Robert Gibbs said Friday that President Barack Obama plans to name a new FDA commissioner and other oversight officials in coming days. Gibbs said they will establish a "stricter regulatory structure" to prevent breakdowns in food safety.
"I think the revelations have no doubt been alarming," said Gibbs. That a company which found salmonella in its own testing would continue to ship products "is beyond disturbing for millions of parents," he added.
FDA officials said they last inspected the Blakely facility in 2001, when it wasn't being used to make peanut butter.
It did not get much attention from the federal government again until earlier this year, when a shipment of peanuts from the plant was returned from Canada because it was contaminated with metal fragments. The FDA then asked Georgia authorities to inspect.
But the state inspections did not detect what FDA officials say was a salmonella problem at the plant dating back to at least June of 2007.
The return of the contaminated shipment of peanuts was first reported by the Associated Press.