Washington ? Federal health officials opened a criminal investigation Friday into the Georgia peanut-processing plant at the center of the national salmonella outbreak. President Barack Obama pledged stricter oversight of food safety to prevent breakdowns in inspections.

The investigation into Peanut Corp. of America follows reports of shoddy sanitation practices and inspections that found the company sold contaminated peanut products to food makers.

At least 529 people have been sickened as a result of the outbreak, and at least eight may have died because of it. More than 430 products have been recalled.

In a statement late Friday, Peanut Corp. expressed its “deepest and most sincere empathy for those sickened” and said it was reviewing the facts to determine exactly what happened.

“Our top priority has been — and will continue to be — to ensure the public safety,” it said. “For Peanut Corporation to engage in any discussion of the facts at this point is premature.”

Until recently, federal food safety inspectors had not been to the Georgia plant since 2001. The Associated Press found that FDA interest in the facility was renewed, at least temporarily, after a shipment of peanuts from the plant was seized at the Canadian border.

The shipment, taken April 11, originated at the Peanut Corp. plant and was turned back at the border. The FDA seized the product after it was found to contain metal fragments.

The seizure was the FDA’s first hint of problems with the peanut products being processed at the Georgia plant. At the FDA’s request, Georgia state inspectors visited the plant on June 10 searching for the source of metal fragments. State inspectors visited again in late October, records show. Neither inspection looked for salmonella.

A few weeks later, federal health officials saw the first signs of a salmonella outbreak. But it took more investigation to identify peanut products as the cause, and the public wasn’t alerted until early this month.

The June inspection focused only on the metal-fragment issue discovered in the shipment to Canada, said Domenic Veneziano, director of import operations and policy for the FDA’s Office of Regulatory Affairs.

Inspectors took no samples of the peanut product for testing during the June inspection or during an Oct. 23 state inspection.

The FDA reported this week that federal inspectors who visited the plant since the salmonella outbreak found roaches, mold, signs of a leaking roof and numerous other sanitation problems.

Federal officials now say the plant had a salmonella problem dating back at least to June 2007. Peanut Corp. was under no obligation to tell the FDA it was making peanut butter at the Georgia plant, the FDA said Friday.