DALLAS (CBSDFW.COM) – Now chipped and cratered, the granite walls of the Earle Cabell Federal Building in downtown Dallas show evidence of the gunfire that erupted Monday. Streets surrounding the building re-opened Tuesday evening, and the building itself will resume regular business Wednesday morning.

Earle Cabell Federal Building in Dallas after shooting (Andrea Lucia -CBS 11)

Witnesses returning to the scene to retrieve cars that had been stuck within the crime scene area recalled being startled by the gunshots.

“We all heard a pop pop pop pop pop, about 8 to 10 shots, sounded like fire crackers actually,” said Robert Davis, who was inside the courthouse for jury duty. Sounds, he said, echoed through the halls, making it difficult to know where they were coming from. He rushed through an open door, taking shelter with about 75 other people in a room with no windows or glass doors.

“It really shook up a lot of people. Especially the first minutes of it coming into the room. A lot folks had got up under some conference tables and things of that nature. Shaking. Some folks were praying,” he said. “And then we had to stay really quiet. You could hear yelling outside the doors.”

He said those inside were able to see video of the shooter, Brian Clyde, collapse outside before making it in the building but agreed not to open a door until they were certain it was safe. Eventually, law enforcement arrived.

Bullets damaged the granite outside the Earle Cabell Federal Building in Dallas (Andrea Lucia -CBS 11)

“The courthouse had plenty of private security there. They were all armed, very professional about what they were doing. Obviously they were the first line of defense and you know they did a great job,” said Davis.

Another witness who watched the attack from his fifth floor apartment said it wasn’t until later he was able to process what happened.

“I lost a lot of sleep last night just thinking of everything,” said Donald Nicholson. “I’m glad we had officers down there to protect us.”

The ATF says it has successfully traced the rifle used by Clyde to the last time it was sold by a licensed dealer. It would not reveal who sold it or to whom, but confirmed it passed that information onto the FBI.

The FBI said it continues to follow up on leads related to the investigation. The motive for the attack remains unclear.