Fire Department investigators have concluded that a fire last weekend at the John Avery Boys and Girls Club was of “undetermined” origin.

The Sunday morning fire destroyed a two-story building across Grant Street from the club’s main building. The club used the building for occasional meetings and storing sports equipment and the club’s records and memorabilia, said Director Sheila Ryba.

All those materials were destroyed, Ryba said.

“This is certainly not what we were looking forward to or needed,” she said. The club’s resources were already strained by the weak economy, she said, but it has received an outpouring of support and help since the fire was reported.

“We are a resilient organization,” she said.

Ryba at first speculated the fire had been set by arsonists, but after looking at the ruined building with fire inspectors she was not so sure.

“I certainly hope not,” she said.

According to Fire Department spokeswoman Sierra Jackson, the building was so damaged it is unsafe to go inside. Investigators ruled out lightning and electrical failure as causes and determined the fire began at the rear of the building.

“It’s tragic and certainly unexpected,” Ryba said.