A man armed with what federal marshals described as an assault-type rifle fired up to two dozen rounds at a West Virginia federal courthouse Wednesday until police returned fire and killed him, state police said.

One security officer within the Wheeling Federal Building was hurt by flying debris, but there were no other injuries, said Chief Deputy Mike Claxton of the Marshals Service in northern West Virginia.

State police spokesman Sgt. Michael Baylous confirmed that the man died from police fire but did not have his identity or any details about him.

Claxton said investigators were seeking a search warrant for the gunman's home in hopes of determining a motive and if he acted alone.

Asked if the gunman had any beef with the U.S. government, Claxton said, "We're really digging hard at this point to find out."

Claxton said the man began firing from a parking lot across from the federal building. "He was observed in the parking lot very quickly after the first shots were fired," he said.

Courthouse security and local police shot at the man. Claxton did not know if there was an exchange of gunfire.

The building houses a variety of courtrooms and related offices, including judges, prosecutors and law enforcement.

The three-story gray federal building remained cordoned off Wednesday night, surrounded by a heavy police presence in the city along the Ohio River in West Virginia's northern panhandle about 60 miles southwest of Pittsburgh.

David Wohlfeil, the owner of the Metropolitan City Grill near the courthouse, said he ran outside after he heard the first round of shots. He heard two more volleys of gunfire then ran back inside.

"I told everyone to get in the basement and then called 911," he said, adding that police arrived while he was on the phone.

Wheeling has been hit by layoffs in the steel industry and its population dropped by 9.3 percent from 2000 to 2010 to about 28,500 people.

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John Raby contributed to this story from Charleston, Larry O'Dell and Steve Szkotak from Richmond, Va., and Brock Vergakis from Norfolk, Va.