NORRISTOWN, Pa.—Investigators say the deaths of two people inside a suburban Philadelphia apartment appear to be a double homicide.

Norristown police say the deaths Sunday afternoon initially appeared to be a murder-suicide but authorities now believe the man and woman were both killed by a third person.

Police chief Russell Bono says authorities were called to the scene around 4 p.m. for an unresponsive person. They found both victims dead inside in a small rental unit.

Authorities did not immediately release the identities of the victims.

Bono says the killings would be Norristown's first murders since last August.