22-year-old Sergio Santiago was taken into police custody at 8:00 a.m. Wednesday at the Neshaminy Inn, located on the Roosevelt Boulevard in Bensalem, Bucks County.
The shooting happened around 3:30 Sunday afternoon on the 1600 block of Wallace Street.
Flores was found in a third floor apartment with a bullet wound to the head. He was taken to Hahnemann University Hospital where he was pronounced dead.
Authorities say Santiago fired a shot at point-blank range while he, Flores and others were in the apartment with some friends.
Police say Flores appears to be a true victim of circumstance.
"He was loving, he was giving. He was honest. He was smart. He was a gentleman," said Wendy Aviles, the victim's sister.
Flores and his sister grew up with Santiago.
"I am completely taken aback, completely taken aback. This was someone who was raised with us, someone we've known for all of our lives," said Aviles.
"Like I said, we know what happened but we don't know why it happened," said Captain James Clark, Philadelphia Police.
Police say while Santiago is known to them, Flores on the other hand, a charter school 11th grader, was a good kid.
That would explain why so many in his neighborhood spent Monday evening stopping by a growing memorial.
Flores' sister says his kindness was perceived as weakness by other teens who would take advantage of him. He was one who saw the good in people like his childhood friend, who is now accused of taking his life.
"As young adults, all young adults make mistakes and we do things we're not supposed to do, but he was not a bad kid," said Aviles.