The shooting scene yesterday "extended over several miles" in Frankstown Township in Pennsylvania, Blair County District Attorney Rich Consiglio said.
Mr Consiglio said the dead were three men and one woman.
Identities of the victims and gunman weren't immediately released.
State police said one trooper was struck by gunfire but escaped serious injury because he was wearing a bulletproof vest.
Mr Consiglio said a second trooper was hit by shattered glass while a third was in a crash involving the gunman.
He said that the public was not at risk.
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