A gunman who was killed by police after firing multiple rounds at a US courthouse was a retired police officer, officials have said.
Mr McKenzie said the retired officer's name was not being released immediately.
US marshals said the man used an assault-type rifle to fire 15 to 25 shots at the Wheeling Federal Building.
One person was injured inside by flying debris.
US Marshals Services chief deputy Mike Claxton said investigators were seeking a search warrant for the gunman's home in the hope of determining the motive and if he acted alone.
Asked if the gunman had any issue with the US government, Mr Claxton said: "We're really digging hard at this point to find out."
He said the man started firing from a car park 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 ultimately returned fire and hit the man.
The building houses a variety of courtrooms and related offices, including judges, prosecutors and law enforcement.
Wheeling police chief Shawn Schwertfeger identified the gunman as 55-year-old Thomas J Piccard, of Bridgeport, Ohio.
Mr Schwertfeger said the retired Wheeling police officer.was armed with an assault weapon and a handgun.
He also said three security officers were injured by flying debris during the onslaught.
Officials said it was too early to tell whether Piccard was targeting anyone in the building or what his motive might have been.
"That's still trying to be determined," said Bob Johnson, the assistant special agent in charge of the FBI's Pittsburgh office.
People inside the building ducked under desks as the shots struck the building and shattered windows.
US attorney Bill Ihlenfeld said shots were fired into at least three rooms in his office on the second floor. He described hearing gunshots, then panic among staff.
"Members of my staff were crawling on the floor or running from office to office telling people to get away from the windows," he said.
Mr Ihlenfeld said he knew Piccard from 1997 when he started working in the city prosecutor's office until the officer retired in 2000. He said he had no reason to believe his office was targeted, and that Piccard was not under any sort of investigation by federal authorities.
"There was nothing about my relation with him or anything that I observed in dealing with him ... to cause me to think anything like this would happen," he said.
About 40 % of Mr Ihlenfeld's staff was laid up because of the federal government shutdown, so many were not working.
"To be honest, the security plans in place to deal with a situation like this don't work when we don't have everybody there," he said.
Carla Webb Daniels said she was in her lawyer's office nearby when she heard loud gunshots. She saw the gunman fire from a bank car park across the street.
"I was so nervous, I couldn't believe it," Ms Daniels said. "People were scared and were banging on the doors asking to be let in."
Piccard's body will be sent to the medical examiner's office in Charleston for a post-mortem. Meanwhile, officials are searching his car, which he drove to the scene, and his trailer across the river in Bridgeport.
Mr Johnson said a bomb squad would clear the home before investigators go in as a precaution.