Scientists at the New York State Food Laboratory on Friday identified aminopterin as the likely culprit in a poisoning scare that prompted the recall of 95 brands of "cuts and gravy" style dog and cat food.

Department of Agriculture and Markets spokeswoman Jessica Chittenden did not know when the lab would have results from the new tests.

The federal Food and Drug Administration has said the investigation into the pet deaths was focused on wheat gluten. Stephen Sundlof, the federal agency's top veterinarian, said Friday it remains the suspected source of the contamination.

Scientists so far have offered no theories on how aminopterin got into the products of Menu Foods, which makes pet food for most of North America's top retailers. Aminopterin, a derivative of folic acid, can cause cancer and birth defects in humans and can cause kidney damage in dogs and cats. Its use as a rodent poison is banned in the United States.

Some pets that ate the food suffered kidney failure, and the company has confirmed the deaths of 15 cats and one dog. The FDA has reported more than 4,400 calls from concerned pet owners.

Cornell University's veterinary school also is testing the food. Dr. Donald Smith, dean of the school, said the tests of the individual food components would likely take days.

"It's a very challenging set of procedures," he said. "We have to keep in mind there are other things out there that could potentially be hazardous. We are working very hard to confirm it was aminopterin."

Scientists at the New York State Animal Health Diagnostic Center at Cornell University and at the New York State Food Laboratory tested three cat food samples provided by the manufacturer and found aminopterin in two of them, the labs announced Friday. The two labs are part of a network created after the Sept. 11 terrorist attacks to keep the nation's animals and food supply safe.

The company recalled products packaged from Dec. 3 to March 6 and advised retailers last week to remove all the products from their shelves to verify the dates they were packaged. Products not made between those dates can still be sold.

FBI spokesman Stephen Kodak said the agency is "not involved in any way, shape, or form." He said the FBI would likely only get involved if evidence pointed to the products being tampered with while on store shelves.

Chittenden said any criminal investigation would have to be initiated by the FDA.

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