Rockne Warren Newell lived alone in the Pocono Mountains of eastern Pennsylvania in utter poverty. His house was on the verge of collapse. His bathroom was a bucket.

But he was intent on keeping his home, even as officials in Ross Township threatened to evict him over the dilapidated property about 100 miles west of Manhattan, which lacked a proper sewage system and was built without the necessary permits. With his only apparent income a $600 monthly Social Security disability check, he argued that he could not afford the court costs to fight the township nor the required improvements and permits.

But the long-running dispute with local government officials reached its end on Monday night, when Mr. Newell, 59, burst into the township’s monthly supervisors’ meeting in Saylorsburg, Pa., firing a rifle, and minutes later returning with a .44 Magnum revolver, killing three, the police said. In all, he fired 28 rounds at the 15 to 18 people inside the room at the time, the police said.