The Food and Drug Administration is investigating​ dog food that tested positive for traces of a euthanasia drug.

​The findings may indicate that companies are using euthanized animals to make their dog food, a practice that is illegal. ​Federal law also states that the drug, pentobarbital, cannot appear in any food.

Pentobarbital is used to euthanize animals and has also been used in doctor-assisted death as well as in carrying out the death penalty.

​The dog food, called Gravy Train, showed trace​s pentobarbital across more than two dozen brands of 62 wet dog food samples, according to Ellipse Analytics, the laboratory that carried out the testing. The firm was hired for the investigation by the Washington, D.C.-based news organization WJLA.

Gravy Train is made by Big Heart Pet Foods which also makes​ the pet foods​ Meow Mix, Milk Bone, Kibbles'n Bits, 9 Lives, Natural Balance, Pup-Peroni, Nature's Recipe, Canine Carry Outs and Milo's Kitchen, Alley Cat, Jerky Treats, Meaty Bone, Pounce and Snausages, ​according to ​KHQ.