Allentown police say the body of 70-year-old John Lebar was found at about 7:45 p.m. Tuesday.
The Lehigh County coroner's office said an autopsy Wednesday determined that he died of blunt force trauma to the head.
Neighbors said they found the body after noticing Lebar's door left open and not finding him inside.
No arrests were immediately reported, and authorities asked anyone with information about the attack to call them.
