The suspect, who was armed with a knife, accosted the security guard, which led the guard to shoot the suspect in the stomach.
The female victim was expected to pull through.
The stabbing was believed to be the product of a domestic dispute, Crump said.
Crump says an investigation is underway.
Dave from Lexington, Maryland, who didn’t want to reveal his last name, was sitting at the McDonald’s waiting for family to arrive on a train from Chicago when he heard the shot.
He said people ran for a back door at Union Station but couldn’t open it, so he and several others locked themselves in a closet.
“Everybody in there was pretty panicky, they were saying ‘don’t talk, stop, shut up, we don’t want anyone to hear that we’re in here’” he said.
Dave said the people in the closet put their feet up to the door, to prevent someone from barging into the room. He could hear people outside pounding on doors as they waited inside the closet. He said they emerged minutes later when the all clear was given.
Chrissie Seredni, of Richmond, Virginia, was in Union Station having lunch with her boss when she heard the shot.
“The first thing she said was ‘oh God, oh God, not now,’” she said.
Seredni said she ran with co-workers from the building and police moved in.
Seredni said she felt from the start that this wasn’t an attack related to 9/11 and quickly her feelings were backed up by police who classified it as a domestic incident.
D.C. police Commander Jeff Brown says there was no apparent connection between the shooting and the anniversary of the Sept. 11, 2001, terrorist attacks.
When police first responded, officials advised people in the area to remain clear of Union Station. The building has since been cleared for people to re-enter.
Also, VRE service is back up after its temporary suspension due to the police activity at Union Station. No other transportation around Union Station has been affected.
Union Station is a massive transit hub and home to Amtrak’s headquarters. The station is bigger than the nearby U.S. Capitol and serves as the southern terminus for passenger rail traffic in the northeast. It includes dozens of retails shops and restaurants, which typically draw thousands of midday diners.
Some 90,000 people pass through Union Station each day, according to Amtrak.
Flags on the towering poles outside the station’s main entrance were flying at half-staff Friday in remembrance of the terrorist attacks on Sept. 11, 2001.
WTOP’s Mike Murillo and The Associated Press contributed to this report.