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 in a shootout, a prosecutor said Thursday.

Two other officers were seriously wounded before police shot the suspect to death in a hail of gunfire that capped a 15-hour ordeal after a trail camera captured an image of the suspect, armed with an AR-style rifle, peering through a scope into the house Tuesday night.

The ex-girlfriend and her mother called the police and then fled the house for their safety after officers dispatched Tuesday night were unable to find him there. Police didn't find him at his own home so arrived back at the house Wednesday afternoon.

Using a drone, six officers scoured the property, including farm buildings, before they noticed the door to the home was unlocked — even though the ex-girlfriend and her mother had locked it before fleeing.

Four plainclothes detectives from the Northern York County Regional Police Department wearing bulletproof vests opened the door and were immediately fired on 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.

Barker said he believed that Ruth had planned to ambush his ex-girlfriend before the detectives walked in.

Ruth fired numerous rounds, killing three of the officers at the door and seriously wounding the fourth, Barker said. A gunfight then ensued between Ruth and two officers outside. Ruth wounded a York County sheriff's deputy before he and another Northern York County Regional officer shot the gunman to death by the road, Barker said.

Detective Sgt. Cody Becker, Detective Mark Baker and Detective Isaiah Emenheiser were killed, Baker said.

All three slain officers were long-time veterans of the nearly 70-officer force, with almost six decades of combined service. Baker, 53, had served 21 years after spending time as a police officer in Philadelphia; Becker, 39, had served 16 years; and Emenheiser, 43, had served 20 years.

The wounded detective and sheriff's officer remained hospitalized, one of whom is in critical but stable condition Thursday.

On Thursday night, a couple hundred people gathered for a vigil honoring the officers at a church in Spring Grove, Pennsylvania, some wiping away tears as pastors led prayers and hymns and a woman sang “Amazing Grace.” Community members wrote messages on stones and arranged them under a table displaying five lit candles. Pastor Brian Kannel of the York Alliance Church helped to organize the vigil.

"You not only are allowed to grieve, you're expected to grieve. And God grieves with you," he said.