Annapolis, MD – At least five people were killed, and many more were “gravely injured,” when a gunman opened fire inside the Capital Gazette building on Thursday afternoon, authorities said.

Authorities said “this was a targeted attack on The Capital Gazette,” The Washington Post reported.

Police have confirmed that the shooter is in custody but did not disclose the gunman’s identity, The Baltimore Sun reported.

According to the WJZ, the uncooperative suspect damaged his fingertips in an effort to avoid being identified by police but investigators have successfully identified him nonetheless.

Anne Arundel County Police and agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives responded to a report of an “active shooter” at approximately 3:15 p.m., The Baltimore Sun reported.

Capital Gazette intern Anthony Messenger was one of the first people to send a tweet about the shooting, WJZ reported.

“Active shooter 888 Bestgate,” Messenger wrote. “Please help us.”

Capital Gazette crime reporter Phil Davis, who was one of about 170 people inside the building at the time of the attack, said that he and his coworkers scrambled for cover as the man opened fire.

“A single shooter shot multiple people at my office, some of whom are dead,” Davis later tweeted as he waited to be interviewed by investigators.

“Gunman shot through the glass door to the office and opened fire on multiple employees,” he wrote a moment later. “Can’t say much more and don’t want to declare anyone dead, but it’s bad.”

Investigators did not specify the type of weapon that was used in the attack, but confirmed it was a “long gun,” according to The Baltimore Sun.

“There is nothing more terrifying than hearing multiple people get shot while you’re under your desk and then hear the gunman reload,” Davis tweeted in a third message.

It was unclear how the suspect was taken into custody, but police said they did not exchange fire with the gunman, The Baltimore Sun reported.

Davis said he and many of his coworkers were still hiding beneath their desks as officers surrounded the suspect and the shooting ceased.

“I don’t know why. I don’t know why he stopped,” he told the paper.

On the building’s fourth floor, Fisher Law Office employees learned of the shooting in a text from a colleague. They barricaded the office door with an overturned desk and waited until SWAT officers arrived.

Investigators have also recovered an apparent “explosive device” and have since “tactically secured” the building, the paper said.

The shooter, who was described as a long-haired white male in his 20s, had flash bangs, smoke bombs, and fake grenades on him at the time of his arrest, WJZ reported.

Anne Arundel County Acting Police Chief William Kramph said that investigators believed the man was the only shooter and said that the agencies were “working to determine what occurred, how it occurred, and why it occurred,” Newsweek reported.

“The investigation has just started, Chief Kramph said.

In the wake of the attack, the New York Police Department dispatched counterterrorism teams to multiple media outlets as a precaution, according to WJZ.

President Donald Trump thanked first responders and expressed his condolences to the victims and their families on Thursday afternoon.

“My thoughts and prayers are with the victims and their families,” the President wrote in a tweet. “Thank you to all of the First Responders who are currently on the scene.”