DALLAS >> A masked gunman opened fire today on a federal courthouse in downtown Dallas before being fatally shot in an exchange of gunfire with federal officers, witnesses and authorities said.

Brian Isaack Clyde, 22, was pronounced dead at a hospital following the shooting outside the Earle Cabell Federal Building. Authorities offered no hint of his motive, but FBI agent Matthew DeSarno said there was nothing to indicate the presence of any other shooters or threats to the city.

Clyde opened fire about 8:40 a.m., and law enforcement immediately responded, including three officers from the Federal Protective Service who were stationed at the building.

A bomb squad later examined a vehicle associated with the gunman as a precaution and performed controlled explosions, authorities said. Two loud blasts could be heard.

The Dallas Morning News reported that one of its photographers, Tom Fox, was outside the building and witnessed the shooter opening fire. Fox said the masked man parked at a street corner, then ran and began shooting at the courthouse. The bullets shattered the glass panes in a revolving door.

An image of the shooter captured by Fox showed the man wearing a balaclava and a heavy vest and carrying a rifle. Several magazines could be seen on his belt.

Another photograph from Fox showed authorities tending to a shirtless man lying on the ground in a parking lot outside the building.

Police closed off several blocks around the federal building.

A woman who answered the phone at a number listed for one of Clyde’s relative declined to comment.

Chad Cline, 46, who lives near the courthouse, told The Associated Press that a message was broadcast throughout his building shortly before 9 a.m. announcing that there was an active shooter in the area and that residents should stay inside.

Less than half an hour later, another message said there was a potential bomb threat and that residents needed to leave. He, his wife and their two dogs went to a coffee shop.