Perusing the website of the American Humane Organization, I came upon a listing of the laws governing euthanasia by state. True to our decentralized mode of government, euthanasia laws are the purview of states, not the federal government. As you can surmise, much of the information deals with which substances and manners of killing are acceptible. Here is the part for New Jersey:
" N. J. Statutes Section 4:22-19.3: Neuromuscular blocking agents prohibited.
When euthanizing a domestic animal succinylcholine chloride, curare, curariform drugs, or any other substance which acts as a neuromuscular blocking agent is prohibited.
N. J. Statutes Section 4:22-19: Destruction of impounded animals.
New Jersey does not allow euthanasia by hypoxia induced by decompression, by lethal gas other than an inhalant anesthetic, or by any other means not generally accepted by the veterinary medical profession.
Penalties: 1st offense (fine of $25 for each animal).
Subsequent offense (fine of $50 for each animal).
New Jersey Administrative Code 8:23A-1.11: Euthanasia.
The primary recommended method is an intravenous injection of a barbiturate. New Jersey also allows administration of injectable solutions approved for use in dogs and cats, inhalant anesthetics, and intravenous injections of combinations of chloral hydrate, magnesium sulfate and pentobarbital for large animals, such as horses. "
Here is the entire PDF: