NEW KENSINGTON, Pa. (AP) — Pennsylvania residents who came to the aid of a rookie police officer who was fatally shot and killed during a traffic stop say he was "gasping for air" and not responsive when they arrived at the scene.

Brian Shaw was shot in the chest around 8:15 p.m. Friday in New Kensington, about 18 miles (29 kilometers) northeast of Pittsburgh. The shooting occurred during a foot chase that began shortly after the traffic stop took place.

Police later recovered an older model of an unoccupied brown Jeep Grand Cherokee, wanted in connection with the shooting. State police said Saturday that investigators know why the suspected shooter was pulled over but would not provide further details, citing the ongoing investigation.

A description of the suspect has not been released.

Shaw had served as a part-time officer in three other towns before joining the New Kensington police force full time in June. He was taken to a hospital after the shooting but was pronounced dead there a short time later, according to authorities.

Nicole Drum, whose family lives directly across from the shooting scene, told The Pittsburgh Tribune-Review that she was on a couch in her living room when she heard six or seven shots, including one that hit her house. She looked outside and saw Shaw fall. She was the first person to reach him.

"I was trying to talk to him," she said Saturday. "He wasn't responding."

Brad Larocca, who lives next door to the Drums, also heard the shots, which he said came rapidly. He said Shaw tried to sit up before collapsing.

"I don't know if he was trying to talk," said Laroccoa, who also tried to help the officer. "He was gasping for air."

Larocca said he didn't know if Shaw also fired his weapon.

"Whichever one was shooting knew how to use a gun. It was quick," Laroccoa said.

Drum said her home was hit twice — once under the front porch, and again on the second floor — but neither shot went inside the house. Her father, Wayne Drum, who was not home when the shooting occurred, said police recovered the bullet that hit the porch on Saturday morning. He was told it was a .40 caliber slug.

The Drum home has a surveillance camera mounted under the second-story eave. Wayne Drum said it had captured everything, but the video was fuzzy since it was taken at night. He said police took his hard drive, telling him they would be able to enhance it.

Police officers from neighboring towns continued to scour the area for the suspect Saturday. SWAT teams and police dogs assisted.

Authorities were offering a $40,000 reward for information on the shooting. The FBI has contributed $25,000 to the reward, while the U.S. Marshals Service offered $5,000 and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives will contribute up to $10,000.

A wake for Shaw will be held Monday and Tuesday, followed by a funeral service Wednesday morning.