26-year-old Darby Borough Officer Mark Hudson was shot in the chest in the second floor of his home in the 600 block of Magnolia Avenue on Saturday afternoon.
His girlfriend, who hasn't been identified, was also in the house at the time of the shooting.
Sources tell Action News that she was taken into custody for questioning.
On Sunday evening sources say the woman was rushed to Mercy Fitzgerald Hospital for an undisclosed medical emergency. No word on her condition.
Police have not named her a suspect but Action News has learned that Delaware County detectives and Darby Township police are at the hospital monitoring her.
"When I first heard about it, I thought something happened in the line of duty but to hear that it was a domestic dispute, that's what really shocked everyone," said Alvin Reese, family friend.
Police say there were ongoing domestic problems and things had gotten so bad, sources say it was Hudson who recently got a protection from abuse order against his girlfriend.
Family and friends are still coping with the loss.
Hudson grew up in Lansdowne. He was known as the guy with an infectious smile who knew what he wanted to do with his life.
"He accomplished his dreams. He wanted to be a fireman, he became a fireman. He wanted to be a police officer, he became one and that's something that really inspired me," said Reese.
Wanda Reese had known Hudson since he was 2 years old.
"He was such a nice spirited young man. Polite, respectful and I just couldn't believe his life was ended so senselessly," she said.
Hudson worked part-time with the Darby Borough Police Department for the last four years.
He was also a volunteer firefighter for the Yeadon Fire Company. He joined when he was just 16.
His fellow firefighters put up black bunting and Hudson's locker and gear are now a memorial.
"It was kind of an around the clock thing for him. He would come up in the middle of the night, after he would get off day work being in a police car all day, for a fire call. He just had a duty to serve and he always did it with a smile," said Chief Michael DiLenno.
Meanwhile, no charges have been filed.
Darby Township Police is leading the investigation.