Andre Gordon, 26, “surrendered peacefully,” Trenton Police Department spokesman Lisette Rios told AFP, after a trail of violence that set off shelter-in-place orders in two states.
Authorities said Gordon, who is believed to be homeless, began the day by carjacking a vehicle in Trenton before driving some 60km to the northern Philadelphia suburb of Levittown.
There, police said, he killed two people – identified as his 52-year-old stepmother and his 13-year-old sister.
Three others in the house, including a minor, managed to hide “as he went through the house searching for them,” Bucks County, Pennsylvania district attorney Jennifer Schorn said in a briefing.
The suspect then drove to a nearby residence where he broke in before shooting and killing a 25-year-old woman – whom Ms Schorn said was the mother of his two children – before bludgeoning her mother with the butt of his rifle. She was expected to recover.
Driving to a nearby discount store, the suspect carjacked a Honda vehicle from a 44-year-old man before fleeing. The man was not injured, according to Falls Township, Pennsylvania sheriff Nelson Whitney.
The suspect then drove across the state line back to Trenton, where he barricaded himself in the three-storey house.
Mr Whitney said the suspect was believed to be armed with a powerful AR-15-style assault rifle.
For several hours, police appealed to him to surrender.
“Andre, get away from the windows. We know you’re inside, if you’d like to surrender, dial 911 now,” police said over a loudspeaker. “You’re a young man, you have too much to live for.”
Later, Gordon was “located at another location in Trenton,” Ms Rios said.
Trenton Police director Steve Wilson said Gordon was uninjured and walking in the street when a patrol officer approached him. It was unclear if he had ever been in the house where police had believed he was barricaded.
Meanwhile, armed Swat officers were seen using a ladder to climb onto the roof of the porch to help people inside the house escape through a window. People in the house were “successfully evacuated with no injuries,” detective lieutenant Rios added.
Because the suspect crossed state lines, federal authorities – including the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives – are aiding in the matter, along with local, county, and state police.