M.G.L. C. 140 § 156
Killing dogs under certain conditions
Any person may kill a dog which suddenly assaults him while he is peaceably standing, walking or riding outside the enclosure of its owner or keeper; and any person may kill a dog found out of the enclosure of its owner or keeper and not under his immediate care in the act of worrying, wounding or killing persons, live stock or fowls.
If any person shall kill or attempt to kill a dog so found, and in the act of worrying, wounding or killing persons, live stock or fowls, he shall not be held liable for cruelty to the dog unless it shall be shown that he intended to be cruel to the dog, or that he acted with a wanton and reckless disregard for the suffering of the dog.
Prompt killing of a wounded dog, or a prompt report to the owner or to a dog officer of the wounding of the dog, shall be considered evidence of sufficient regard for the suffering of the dog.
M.G.L. C. 140 § 158
Killing unrestrained dogs or dogs in wild state
Elements:
Any police officer, constable or dog officer
shall kill a dog
which the selectmen of a town, chief of police of a city, or the county commissioners,
or, upon review, the district court,
shall have ordered to be restrained
if such dog is again found outside the enclosure of its owner or keeper and not under
his immediate care,
and may kill a dog which is living in a wild state.