Bloomfield, listed for sale last year at $6.9 million, had 19 bedrooms and nine full baths in its 22,000-plus square feet of living space, officials said.
The mansion with decorative gardens is on South Ithan Avenue near Villanova University.
Wood said the fire originated in electrical wires stapled to the cellar wall in an area beneath the garage adjacent to a laundry room.
At first, it was confined to the ceiling beneath the first floor, but then traveled horizontally to an area between the laundry and breakfast rooms.
"There was a dumbwaiter there with a void in it, and the fire went from the basement through the former dumbwaiter shaft to the attic area," Wood said.
From there, the fire spread sideways throughout a storage area on the third floor.
Others said the slate roof acted as an oven, keeping the heat under wraps until flames consumed the third floor, finally causing the roof to collapse on arriving firefighters. Some were treated for minor injuries.
Immediately after the six-hour blaze was declared under control, Wood and Radnor police began investigating.
They called in the State Police, Delaware County investigators, and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives to help.
Wood said that all of the wiring was replaced 10 years ago, according to an inspection sticker on a circuitbreaker box. There was no need for a more current inspection.
He described his investigation as complete, with no need for any official action.
At the time of the fire, the mansion was occupied by Julie Charbonneau, a Canadian interior designer who specializes in high-end redecoration projects involving French or country-style houses, and Dean Topolinski, a Montreal business mogul. The two have a young daughter, Alexia.
They moved in last August under a lease-purchase accord with owner Jerald S. Batoff.
When the fire broke out, the family and pets escaped without harm, as an automatic alarm summoned firefighters. But since then, their whereabouts have been unclear.
All three phone numbers listed to the mansion's address were no longer in service. Charbonneau did not return an e-mail or a call to her Web-based business in Montreal. A secretary said she would return the week of April 22.
Contact Bonnie L. Cook
at 610-313-8232 or firstname.lastname@example.org. Read her "MontCo Memo" blog at www.philly.com.