A federal investigation has concluded that fires in late January that seriously charred a conservative think tank's Golden Valley headquarters and other offices in the building were intentionally set.

The blaze at the Center of the American Experiment was detected about 2 a.m. on Jan. 28 at its headquarters just south of Interstate 394 and east of Hwy. 169. The think tank's spokesman, Bill Walsh, said two other conservative organizations in the same building, the Upper Midwest Law Center and Take Charge, were also targeted by what American Experiment has described as a firebombing.

The federal Bureau of Alcohol, Tobacco and Firearms and Explosives (ATF) said in a statement released Wednesday to the Star Tribune that one of its fire investigators officially determined that "the fires were intentionally set" on the first and third floors. There have been no arrests.

The ATF statement said its investigation remains active and involves other agencies in pursuit of "actionable leads."

Tips about the fire can be submitted to the ATF at 888-ATF-TIPS (888-283-8477) or ATFTips@atf.gov.

Independently, the center has a reward for information that leads to those involved in setting the fire. The center said there is a reward of $50,000 if one person is convicted and an additional $50,000 if two people are convicted.