(CNN) - The FBI is investigating the military background and social media history of a 22-year-old man who is suspected of trying to shoot up a federal building in Dallas Monday.
Brian Isaack Clyde was shot and killed by federal officers before he got a chance to enter the Earle Cabell Federal Building, authorities said.
No officers or other citizens were injured in the shooting on the south side of the building, police said. One worker sustained a superficial injury when she was taking cover, US Attorney Erin Nealy Cox said. She added that there were 300 federal workers inside the building during the shooting.
Clyde was taken to a hospital where he was declared dead, according to FBI special agent in charge Matthew J. DeSarno.
DeSarno said at a press conference that Clyde was discharged from the Army in 2017. The US Army confirmed to CNN that Pfc. Brian Clyde served as an infantryman from August 2015 to February 2017.
The FBI is working with the Department of Defense "to examine his record and identify any associates," DeSarno said. The shooter's firearm was also recovered and federal authorities are working with the ATF trying to trace the gun's origins and how the shooter obtained it.
DeSarno also said the suspect had more than five 40-round magazines on him. Authorities don't believe he entered the courthouse, DeSarno said. Agents all over the state are interviewing relatives and associates so the FBI can find a motive, DeSarno said.
"We have more than 200 FBI agents and partners aggressively pursuing every lead in this investigation in order to identify his family members, associates and get to the bottom of what the motive was," DeSarno said.
Prior to today's shooting, DeSarno said Clyde was not of "investigative interest" to the FBI. Agents are still working to see if Clyde was known to any other law enforcement agencies.
Authorities said Monday they were "aggressively pursuing" Clyde's social media activity, according to CNN affiliate KTVT.
Police also said a bomb squad was preparing to do a controlled explosion of the suspect's vehicle, the vehicle has been deemed safe and is in their custody. DeSarno said there was no indication that there are other shooters or threats.
One witness, Don Myles, told CNN affiliate KTVT he was walking into the courthouse when a group of people ran out and he heard about 10 to 15 gunshots in rapid succession. Myles said he turned and ran across the street to safety.
"It was just a whole lot of shots going on," Myles said. "It scared me to death."
Another witness, Herman Turner, told KTVT that the gunman was wearing fatigues and his face was covered by a mask.
The Earle Cabell Federal Building will be open on Tuesday for employees but closed for business, according to a tweet from the FBI. This means there will be no hearing or public services.
CNN's Jamiel Lynch and Ryan Browne contributed to this report.
The-CNN-Wire ™ & © 2019 Cable News Network, Inc., a Time Warner Company. All rights reserved.