The shooting of a man who went on a rampage in Pennsylvania, killing two neighbours and a third person before wounding three state troopers, was a justifiable homicide, authorities have ruled.

Investigators are still trying to determine why the gunman, identified as Jeffrey Michael, 44, of Geeseytown, a tiny village west of Harrisburg, the state capital, went on his murderous spree.

"We're not sure of the motive. We'll be trying to find out by talking to people who knew him, see if he gave any indication," district attorney Richard Consiglio said.

The killings began on Friday morning in Frankstown Township and spanned five separate crime scenes across a 1.5-mile area.

Authorities said Michael knew his two male victims, who were related to each other, but investigators do not yet know whether he knew the third, a woman gunned down while decorating a church hall for a children's Christmas party.

Michael fired into the Juniata Valley Gospel Church from outside, then entered the church and fired again, killing Kimberly Scott, 58, of Duncansville, state police sergeant Gregory Bernard said.

Either shortly before or after that, Kenneth Lynn, 60, a neighbour of Michael, was shot in the driveway of his home.

Sgt Bernard said Michael drove his pick-up truck along rural Juniata Valley Road and intentionally rammed another pick-up driven by Mr Lynn's son-in-law, William Rhodes, 38. Mr Rhodes died of blunt force trauma from the crash and from a gunshot wound, police said.

Michael was leaving the area in his truck when he saw two state police cars heading his way and opened fire as he was passing them, police said. One round went through the windscreen of one of the patrol cars and a trooper was injured in the face by flying glass and possibly a graze from the bullet, they said.

Both troopers turned around and gave chase and a third patrol car tried to block the path of the pick-up, which rammed the car head-on, injuring the trooper driving. One of the other patrol cars then rammed the back of the truck and a gun battle with the first two troopers followed.

One officer was hit in the chest and wrist during the shoot-out. "His body armour saved his life," Sgt Bernard said.

The suspect was struck by police gunfire and was pronounced dead at the scene. The three troopers were treated in hospital but were expected to make full recoveries, authorities said.

The district attorney's office classified Michael's death as a justifiable homicide and said it would not pursue criminal charges against the troopers.

Police have not released information about the weapon or weapons used by Michael. Sgt Bernard said police had had some contact with Michael but declined to go into detail.

"We've had other incidents, but nothing to this extent," the he said.

Online court records show no criminal record for him in Pennsylvania or in the state's federal courts.

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