Police in Pennsylvania are investigating why a man shot dead three people, including a woman decorating a church hall for a children's Christmas party.
The gunman opened fire on a rural road in Frankstown Township on Friday and was killed in a shoot-out with state troopers after crashing his car into one of their vehicles.
Three officers were injured, including one who was shot in the wrist and chest and another who was left with glass fragments in his eye.
Investigators examined five crime scenes within a 1.5-mile radius as they searched for a motive for the attacks.
Trooper David McGarvey, a state police spokesman, said: "We don't believe it was a domestic dispute but we also don't know a motive, because the shooter was not related to any of the victims."
""It's going to take us some time to put this all together," added Lt Col George Bivens, a deputy state police commissioner.
Shortly after shooting a woman at Juniata Valley Gospel Church, the gunman killed two men at their respective homes before leaving the area in his pick-up truck.
He was shot dead after opening fire at two police cars heading to the scene of one of the shootings and crashing his vehicle head-on into a third patrol cruiser.
"I think we have three very fortunate state police members tonight," Lt Col Bivens added. "We are very thankful for the fact they survived this attack. Someone was watching over them."
The violence unfolded as many Americans observed a moment of silence for the 20 children and six adults shot dead at Sandy Hook Elementary School in Newtown, Connecticut.
The victims of the Pennsylvania shootings, which are not thought to be connected to events in Connecticut a week ago, have not yet been identified.