DALLAS, Texas - Authorities say a masked gunman who attempted an attack on the Earle Cabell Federal Courthouse in downtown Dallas on Monday was shot dead by officers. The FBI identified the man as Brian Isaack Clyde, 22, a former Army private who served for two years.

The FBI said Clyde was killed in a gunfight with federal security officers outside the building. CBS Dallas/Fort Worth reports dozens of Dallas Police Department squad cars and emergency vehicles from Dallas Fire Rescue were on the scene after the active shooter situation at the building in the 1100 block of Commerce Street.

At a press conference, FBI Dallas Special Agent in Charge Matthew DeSarno said, "Shortly after the incident began this morning officers from the Federal Protective Service engaged the shooter who was later identified as Brian Isaack Clyde. He was taken to Baylor hospital and pronounced deceased on scene."

"The federal building was shot on by an active shooter," U.S. Attorney Erin Nealy Cox said. "Law enforcement responded immediately and I want to assure the community, especially our downtown community, that the community is safe."

Cellphone video captured by Dallas resident Tim Brown shows a masked person outside, armed with some type of long gun, firing near an entrance to the building. The sounds of gunshots can be heard and smoke can be seen coming from several feet away, as the gunman runs across the street into a parking lot and collapses.

The suspect was given medical attention at the scene and then taken to a local hospital where he was pronounced dead. Clyde's vehicle was found nearby and a police bomb squad examined it "for precautionary reasons." Several minutes after examining the car with a robot, police decided to blow up the vehicle.

After the shooting, witness Don Myles told CBS DFW, "I just saw a burst of people running out and a round of shots. It was just shots, maybe 10 to 15 shots all rapid shooting, and I just ran across the street into the traffic."

All of the streets surrounding the federal building were closed after the shooting. Officials say no officers or citizens were injured during the incident.

Because the shooting happened on government property, the investigation has been handed off to the FBI. They will be assisted by the ATF, Federal Protective Service, U.S. Marshals and the Dallas Police Department.

CBS Dallas/Fort Worth reported Clyde posted extensively about guns and ammunition on Facebook prior to the shooting.