The man's body was found in a car parked in the detached garage behind a 2½-story home at 44 Seger Ave. Wednesday, they said.
Firefighters doused the heavily-involved blaze, which was called in at 5:42 p.m.
No other injuries were reported.
The cause hadn't officially been determined, Passaic County Prosecutor Camelia M. Valdes, Clifton Police Chief Thomas Rinaldi and Clifton Fire Chief Frank Prezioso said in a brief release.
An investigation was continuing.
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