N.J. Stat. § 45:16-15
A veterinarian or boarding kennel may elect the humane disposal of an unretrieved animal no sooner than 4 days after the owner or agent thereof has signed or refused to sign for the receipt of a certified letter from the veterinarian or boarding kennel owner indicating intent to humanely dispose of the animal, which letter shall be sent to the owner's or agent's last known address. In the event the owner cannot be notified by certified mail, return receipt requested, the veterinarian or boarding kennel owner may elect humane disposal any time after 4 days following return of the certified mail receipt. The veterinarian or boarding kennel manager shall keep an accurate record of the date and method of disposal and the name, address and telephone number of the person or shelter receiving the animal.
N.J.S. § 45:16-15