Rat poison has been found in tainted pet food that sparked a nationwide recall of "Menu Foods" pet food.
Now, the FDA is trying to figure out where it came from and who is responsible.
New test results show aminopterin, a type of rat poison could be to blame for the massive pet food recall in the United States.
Dan Rice, an employee at a food lab, stated "We have no idea how it could have gotten into the food product."
While the toxin is used to kill rats in other countries, it is only legal to use as a cancer-drug here in the US.
Agriculture Commissioner of New York, Patrick Hooker, said "There are any number of ways to contaminate food."
The Food and Drug Administration is focusing on wheat gluten in the pet food that's suspected of causing kidney failure in dogs and cats across the country; killing at least 16, including 15-month-old Abby.
Pet owner Pam Sims said, "To see her deteriorate was very hard. In the end I literally carried her into the vet."
Those deaths led to the recall of 60-million cans and pouches of pet food made by Menu Foods under more than 95-brand names.
Sims added, "It's hard, we do feel guilty because we trusted. You just trust it's going to be safe."
Even though pet owners and veterinarians may now know what caused the contamination, they still have to wait for answers about how it happened.
A complete list of all tainted pet food products along with product codes, descriptions, and production dates can be found on the Menu Foods website by visiting the link below.