SHAMOKIN (AP) - A central Pennsylvania man shot his mother and another man to death before turning the weapon on himself in a Shamokin apartment, authorities said Sunday.

Joananne Grodzki, 42, of Shamokin, and Richard Erb, 36, of Coal Township, were shot by Richard Zimmerman Jr., 20, of Shamokin, who then killed himself, the Northumberland County coroner's office said.

All were pronounced dead at the scene, each of a single gunshot wound to the head, the coroner's office said in a statement. Shamokin police said a 20-gauge shotgun was used.

Police said Zimmerman is Grodzki's son, and they are investigating what led to the shootings at about 6 p.m. Saturday. Cpl. Jarrod Scandle said that after the gunman shot the victims, he briefly left the ground-floor apartment of the three-story building but then returned and shot himself.

Neighbor George Gruneberg said he heard two "large bangs" coming from the apartment but thought it could have been a steel door slamming or a faulty furnace.

"I stepped out the door then to see what was happening and a policeman told me to get back inside the house," he said. Gruneberg said he was later told to evacuate, as were other neighbors as police closed several blocks to traffic and pedestrians.

Relatives and friends, some weeping, stood outside the home for hours as emergency responders worked at the scene.