A man in a dispute with the Social Security Administration opened fire with a shotgun in a downtown Las Vegas federal building Monday, killing a security guard and wounding a U.S. marshal.

Two law enforcement officials told The Associated Press the gunman was Johnny Lee Wicks, 66, who was killed in a gun battle by marshals who chased him across Las Vegas Boulevard. The officials spoke on condition of anonymity because they weren't authorized to discuss the case.

Wicks filed a benefits complaint in April 2008 against the Social Security Administration but lost his claim in September, court documents say.

"We don't believe it's terrorist related at all. It looks like a lone criminal act," FBI Special Agent Joseph Dickey said.

The gunman fatally shot Stanley Cooper, a retired Las Vegas police officer who served 26 years on the force before becoming a court security officer in 1994, U.S. Marshals spokesman Jeff Carter said. U.S. Marshals did not release the name of the wounded marshal, who was being treated at University Medical Center in Las Vegas.

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Donna Leinwand reports for USA Today.