The incident happened around 7:00 p.m. at the Hanover Garden Apartments.
Investigators say crews were responding to a fire that was quickly brought under control when a body was found.
They also discovered blood that was smeared on the wall of the staircase leading to the second-story apartment.
Authorities say the victim has been identified as 17-year-old Kevin Allen, a high school junior from Norristown, Pennsylvania.
"In this case the murderer made some mistakes, so we have some leads to work on," said Chester County D.A. Tom Hogan. When asked if Allen was targeted, Hogan said "It does not appear to be a random attack."
The apartment belongs to the victim's father, who shared parental custody of the 17-year-old with the boy's mother, who lives in Norristown. Allen's father was not at home at the time.
Hogan said it was not unusual for Allen to visit his dad.
"They're devastated that they lost a 17-year-old son," Hogan said of Allen's parents.
There was no word on exactly how Allen was killed. An autopsy is planned for late Wednesday.
North Coventry police and Chester Co. detectives are investigating. Anyone with information should contact them at (610) 323-8360 or (610) 692-5100.