The father was released Tuesday afternoon after being questioned by police.
This case is now in the hands of the Philadelphia District Attorney to decide what - if any charges - should be filed against him.
Police were called to the Holme Circle Apartments in the 2800 block of Axe Factory Road around 11:30 last night to a second floor apartment where a 41-year-old man lives with his 20-year-old daughter.
Philadelphia Police Chief Inspector Scott Small says, "Upon police arrival, they found a 32-year-old male who was shot one time in the head."
He was pronounced dead at the hospital a short time later.
The initial report was that the he was an intruder who'd broken into the apartment and was shot by the homeowner when he found him in his daughter's bedroom.
Police say the man climbed through the second story window, but now say it seems he wasn't an intruder - he was the 20-year-old daughter's boyfriend she invited into the apartment.
Her father woke up when he heard a noise in her room, went to investigate, and found a man he'd never seen before crouching near her bed.
He told the stranger to get down, stay still, and called 911.
Sources say the father was on the phone with a dispatcher when the man moved. The father fired once - shooting him in the head.
Father and daughter were taken in for questioning.
Captain James Clark of Philadelphia Police says, "We're still investigating it. We're keeping the district attorney's office updated of all our information and a decision will be made today on whether there's an arrest or not."
Neighbors never heard a thing - and were surprised to learn that there had been a gun fired on their quiet street.
Neighbor Allen Wasnick says, "To me it seems to be a family type of thing and I don't feel threatened by it at all."
The father and daughter spent all night and all day being questioned by homicide detectives. They were allowed to go home Tuesday afternoon.
No charges have been filed, although the case remains under review by the district attorney.