Police tape blocks a section of a cornfield Thursday near where police were shot during a domestic investigation on Wednesday in North Codorus, Pa. (AP Photo/Tassanee Vejpongsa)

NORTH CODORUS, Pa. (AP) — A suspected stalker armed with a rifle hid inside his ex-girlfriend’s home in the rolling farmland of southern Pennsylvania and ambushed police officers who came to arrest him, killing three of them, a prosecutor said Thursday

Police arriving at the scene at about 2:10 p.m. Wednesday noticed the door to the home was unlocked even though the ex-girlfriend and her mother had locked it before leaving for their safety.

The plainclothes detectives wearing bulletproof vests opened the door and were immediately fired upon by the suspect, 24-year-old Matthew James Ruth, who was carrying an AR-style rifle with a suppressor, York County District Attorney Tim Barker said.

He said the suspect fired multiple rounds, killing three of the officers at the door. A gunfight then ensued between Ruth and two officers outside. Ruth wounded a sheriff’s deputy before police shot the gunman to death, Barker said.

Detective Sgt. Cody Becker, Detective Mark Baker and Detective Isaiah Emenheiser were the officers who were killed, he said. All the officers involved worked for the Northern York County Regional Police Department.

“Each of these men represented the best of policing. They served with professionalism, dedication and courage. They were leaders within our agency, committed to protecting this community and standing beside their follow officers,” Chief Dave Lash said.

Investigators also discovered the ex-girlfriend’s dog had been shot dead in the basement.

How the shooting unfolded

The violence erupted Wednesday afternoon as officers sought Ruth, who they believed had been at the property the night before. A woman he had briefly dated lived there. Her mother called police late Tuesday after she spotted a man wearing camouflage looking into the home with binoculars.

Officers also spoke with the daughter, who had a photo from a trail camera showing someone carrying a rifle outside and aiming a scope at the house, according to a police affidavit.

Ruth eluded police that night, leading them to return the next day with misdemeanor warrants for his arrest. The young woman’s car had been set on fire in August and she said she suspected he may have been involved.

Investigators went to Ruth’s home in Hanover, about 10 miles from where the officers were killed, at about noon on Wednesday and talked to relatives, Barker said. He was not there, so they left at about 1:20 p.m. to try the ex-girlfriend’s home again.

They returned to Hanover after the shooting and left with several bags of potential evidence, neighbor Rose Miller said. She didn’t know Ruth well, but remembered him working on Boy Scout fundraisers. No one answered the door at the home on Thursday.

A community mourns

“We need to do better as a society,” Gov. Josh Shapiro said Wednesday evening. “We need to help the people who think that picking up a gun, picking up a weapon is the answer to resolving disputes.”

It was one of the state’s deadliest days for law enforcement this century, matching the toll from a shooting in 2009 when three officers were ambushed by a domestic violence suspect sporting a bulletproof vest.

Community members held American flags and saluted as police and emergency vehicles formed a procession to the coroner’s office, and people left flowers outside the slain officers’ headquarters.

The confrontation unfolded on a rural road in North Codorus, about 46 miles north of Baltimore.