Hours after resigning from the Colwyn police force, a man fatally shot his ex-girlfriend and wounded her 15-year-old daughter at their home in Glenolden on Monday night, officials said.

Delaware County District Attorney Jack Whelan said his office could seek the death penalty against Stephen Rozniakowski.

The 9 p.m. shooting occurred just hours after Rozniakowski was served with a protection-from-abuse order for Valerie Morrow.

Whelan said Rozniakowski had been "obsessively" stalking Morrow since she ended a relationship with him and returned to her husband in the summer.

Rozniakowski had a plan, the prosecutor said.

"It was his intent that day to arm himself with a gun, to arm himself with a bulletproof vest, and to execute all three family members and take down whoever got in his way," Whelan said at a news conference in Media.

Rozniakowski parked a block from the family's house on Glenfield Avenue, then sneaked to the front door, according to the prosecutor. He then allegedly kicked down the door to the house where Morrow, 40, lived with her husband, Tom, and her daughter, then went upstairs and shot mother and daughter.

Valerie Morrow was killed on the spot. Her daughter was wounded in the left arm and fled to her bedroom.

Tom Morrow, a part-time police officer in Morton, got his revolver and shot and wounded Rozniakowski before jumping out a second-story window to get help, believing his wife and stepdaughter were dead, officials said.

The girl then came out of her room, saw Rozniakowski bent over with his gun near his head, kicked the gun out of his hand, and ran from the house, Whelan said.

The teen and Rozniakowski were treated at Crozer Chester Medical Center. Rozniakowski was in critical but stable condition Tuesday afternoon. Tom Morrow was treated for a fractured ankle and released Monday night.

During the incident, Rozniakowski used the police radio to call 911 and tell the dispatcher what had happened, including that he was the shooter.

He faces charges including murder and attempted murder.

"This is horrifying for law enforcement here in Delaware County," Whelan said.

jmcdaniel@phillynews.com 610-313-8205 @McDanielJustine