Sitting in the living room of her family’s 19th-century colonial home, Lesley Fowks recalled the day in 2002 that her son, Ian Brady, burst in with an announcement: the rusting 1977 Volkswagen camper van sitting in the side yard of a nearby house could be his “for free.”

The young man, then 13, explained that he’d be doing yard work in exchange for the nonrunning vehicle. Well aware of her son’s infatuation with this derelict VW, Ms. Fowks walked with him to the house, a block away, to investigate.

The camper had been parked under the same tree since she; her husband, Tom Brady; and Ian moved into the neighborhood in 1991. At the time, Ms. Fowks didn’t know anything about the camper’s owner, James Rose, who had died that year at 78.

Nearly obscured by a curtain of trees, the house on East Ridgewood Avenue was also a mystery.

“It looked dilapidated,” she said. “We thought it might be abandoned. People called it the ‘tree house’ because it was built around the trees on the property.”