The rented cabin on Ratzer Road had "debris everywhere," a responder said. "We're unsure if it had running water or even heat or electricity."
Firefighters battled valiantly, but the 7:42 p.m. blaze quickly went to three alarms as flames blew through the roof.
Robert Freudenberg and his dog, Popeye, were later found dead inside.
All five township fire companies responded, along with a warming bus and the Wayne Township Memorial First Aid Squad.
A PSE&G crew also was summoned.
The Passaic County Prosecutor's Office was investigating the cause.
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