"Officer Brian Shaw, you were taken from us too soon", the department wrote.
Gov. Tom Wolf has ordered all commonwealth flags on the Capitol Complex and throughout Westmoreland County to fly at half-staff to honor fallen Police Officer Brian Shaw.
The shooting occurred around 8 p.m. Friday in New Kensington, about 30 kilometers northeast of Pittsburgh.
Police have identified the shooter as 29-year-old Rahmael Sal Holt and released a photo of him on Twitter late Saturday evening.
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Residents and multiple law enforcement agencies contributed funds to offer a $43,500 reward for information leading to Holt's arrest.
Police have not said why Holt was pulled over, or why he ran away.
According to Fox News investigators are still determining the reason why Shaw initiated the traffic stop in the first place, but authorities declined to provide further details while the investigation is underway.
Police officers from neighboring towns, some carrying rifles, are scouring the area for the suspect.
Police have recovered a brown, older model Jeep Grand Cherokee wanted in connection with the shooting.