A chemical found in recalled pet food may have been put there intentionally.
That is one theory the FDA is investigating, as it tries to pinpoint what exactly killed dogs and cats who ate various pet foods.
An industrial chemical called melamine, which is used in plastics, was found in an ingredient in the foods.
Investigators believe it may have been added to make the food appear to be more protein-rich than it truly was.
FDA Continues Investigation into Tainted Pet Food