A reward is being offered in hopes of finding whoever is behind what Minneapolis park officials are calling three cases of arson since the historic John H. Stevens House first caught fire in late August.

The city Park and Recreation Board said Thursday that anyone providing information leading to the identification of those responsible for the fires will be eligible for a reward of up to $5,000 through the Minnesota Department of Public Safety State Fire Marshal Division.

Tipsters can call 1-800-723-2020 or notify Park Police Lt. Mark Swanson at 612-230-6561 or parkpolice@minneapolisparks.org.

While the Park Board is calling all three fires arson, the Minneapolis Fire Department so far has publicly declared that only one was intentionally set.

Assistant Fire Chief Melanie Rucker said last week that an arson was to blame for the Sept. 20 blaze at the building in Minnehaha Falls Regional Park.

"Fire patterns and a positive indication for accelerant indicate that this was [an] intentionally set fire of the exterior of the structure," Rucker said in a statement.

On Friday, however, board spokeswoman Robin Smothers said the Fire Department has classified the second and third fires as arson, too. "Based on the pattern, Park Police are investigating as though [the first fire] was also intentionally set," Smothers said.

The most recent of the three fires occurred Oct. 1, when crews responded shortly before 4 a.m. to find heavy fire rising from a rear corner of the building. Crews cut through a fence and boarding to douse the blaze, which burned the building's first and second floors as well as the roof near the chimney.

The building's first fire occurred Aug 30. Fire crews found flames on the back side of the building burning through a first-floor wall. The blaze was extinguished before it could spread.

No injuries were reported in any of the fires.

The Stevens House was built from 1849 to 1850 near where the Minneapolis post office now stands. It soon became a meeting place for early settlers, who went on to found Hennepin County. The city's Park Board took ownership of the house later that century and moved it to Minnehaha Park.