City police aren't identifying the boy who lived in the downstairs apartment with his mother and two brothers. The boy is undergoing a psychiatric evaluation but cannot be charged with a crime in Pennsylvania because he's under 10.
Police say the boy's mother apparently tried to put out the fire before calling 911 and fleeing with her children.
The fire started about 2 a.m. Wednesday and killed a man and woman who lived in a third-floor apartment in the same converted house.
The Allegheny County medical examiner has yet to release their names or causes of death.
