In an AP article by Mark Johnson, it's revealed that a laboratory in Albany New York has identified the poison that caused the deaths of many pets. The scientists at NY Food Laboratory named aminopterin as the chemical responsible. A derivative of folic acid, aminopterin can cause birth defects, cause cancer, and bring kidney damage to dogs and cats. Its used as a rat poison and is also banned in the United States.
read more about it here: http://hosted.ap.org/dynamic/stories/P/PET_FOOD_RECALL?SITE=MELEE&SECTION=HOME&TEMPLATE=DEFAULT&CTIME=2007-03-26-16-43-13NY