In an 8 p.m. ET news conference, police said a white man in his 30s entered the building with a shotgun and fired on people on the lower level. Five people are confirmed dead, and two people sustained superficial injuries.
The victims were identified as Rob Hiaasen, 59, a former feature writer for The Baltimore Sun who joined the Capital Gazette in 2010 as an assistant editor and columnist; Wendi Winters, 65, a community correspondent who headed special publications; Gerald Fischman, 61, the editorial page editor; John McNamara, 56, a staff writer who had covered high school, college and professional sports for decades; and Rebecca Smith, 34, a sales assistant hired in November, the Capital Gazette reports.
The suspect used smoke grenade canisters when he entered the building.
The suspect lives in Maryland, and authorities were preparing to search the man's residence, police said.
Police said threats were sent to the Capital Gazette through social media possibly as recently as today. The threats "indicated violence."
Police said they have no knowledge any specific person was targeted.
Police said earlier reports about the suspect mutilating his fingers in an attempt to alter his fingerprints are not confirmed.
The suspect is Jarrod W. Ramos, a 38-year-old Laurel man whith a longstanding dispute with the Capital, according to law enforcement sources familiar with the investigation, the Capital Gazette reports.
His dispute with the Capital began in July 2011 when a columnist at the paper covered a criminal harassment case against him. In 2012, Ramos brought a defamation suit against the columnist and the paper's former editor and publisher. In 2015, Maryland's second-highest court upheld a ruling in favor of the Capital Gazette and a former reporter who were accused by Ramos of defamation.
Anne Arundel County Executive Steve Schuh told CNN the suspect was found hiding under a desk, possibly trying to hide from police, and that the gun was not in the immediate vicinity of the suspect.
Schuh said four victims died in the building at the scene and one victim died at the hospital during treatment.
Anne Arundel County Police Lt. Ryan Frashure said the suspect was being interviewed by detectives.
The building is secure, according to officials. A bomb squad did recover what they thought was an explosive device, an official said. That item was "taken care of."
It was unclear where the shooting occurred in the building, officials said. The newspaper is one of several tenants in the building.
Lt. Frashure said the detained shooter is the only suspect in the incident. The type of weapon used in the shooting was not immediately known, police said.