Police are executing a search of an address associated with the suspect, law enforcement officials tell CNN.
They believe the suspect had a some interaction with an executive at the newspaper previously, one of the sources said. The source cautioned that this is preliminary information, and the investigation is just beginning.
The suspect is described as being in his 30s.
Annapolis Mayor Gavin Buckley revealed that the suspected incendiary device was a bag containing multiple gas cans in an interview with CNN’s Erin Burnett on “Out Front.”
Buckley called today's shooting devastating. He said police were at the scene of the shooting within 60 seconds.
"If they didn't get there as fast as they did, I think there could have been a lot more devastation," he said.
First lady Melania Trump, returning from Arizona, has tweeted about the shooting in Annapolis, Maryland, saying it was "tragic" and "evil."
Some background: Trump was in Arizona to “learn and educate herself” about issues at the border.
She met with US Marshals, border patrol agents and ICE agents. The first lady also visited small children and babies at a facility.
White House press secretary Sarah Sanders denounced the shooting in Annapolis, Maryland, tonight, saying an attack on "journalists doing their job is an attack on every American."
The suspect’s fingerprints appear to have been altered, making it difficult to identify him that way, two law enforcement sources said.
The suspect was identified using facial recognition software, according to one law enforcement source.
Maryland Gov. Larry Hogan just released a statement about today's shooting at the Capital Gazette in Annapolis, Maryland.
"We are terribly saddened by the loss of five members of our community in today's heinous shooting," Hogan said.
He thanked first responders who arrived at the scene within moments of the shooting.
Hogan also spoke about the newspaper and the journalists who work there.
"The Capital Gazette is my hometown paper, and I have the greatest respect for the fine journalists, and all the men and women, who work there," he said. "They serve each day to shine light on the world around us so that we might see with more clarity and greater understanding."
An employee on lockdown in a nearby building during a shooting at the Capital Gazette in Annapolis, Maryland, described the frantic moments that unfolded at the scene.
Daria McMiller, who works as an administrative assistant in a building next to the Capital Gazette building, said responding officers “were hustling."
McMiller said she and her coworkers didn’t hear any shots, but they did hear police yelling. They saw police, FBI, state troopers and SWAT respond to the scene. She said they weren’t getting any information, but were able to call their loved ones as they waited.
McMiller, a US Marine who is no longer active duty, said her first thoughts were “just to keep my coworkers safe, keep everybody inside and quiet.
"I didn’t even think about how stressful this was until we were all sitting around," she said.
Right now we don't know if this newsroom was targeted or not, but we know that four of the five people who died were pronounced dead in the newspaper office. The fifth person died at the hospital.
Threats against journalists have been on the rise in recent years. Press freedom groups have also reported an uptick in physical assaults on journalists, particularly at campaign events and other political venues.
But, thankfully, murders of journalists are very rare. That's one of the reasons why this day is so shocking. In some ways, it harkens back to the WDBJ shooting in Virginia in 2015, when two members of a TV news crew were attacked and killed by an ex-employee while on live TV.
In the wake of that attack, and the general rise in threats, many newsrooms have stepped up emergency drills and taken other measures to increase security. But newsrooms are inherently open and journalists strive to be accessible. Some sick person exploited that openness today.
Two people injured in the shooting at the Capital Gazette were transported with minor injuries to Anne Arundel Medical Center in Annapolis, Maryland, hospital spokesperson Loren Farquahr said.
The victims did not suffer gunshot wounds, and one was released from the hospital, Farquahr said. The other patient is expected to be released this evening.
A third person from the Capital Gazette shooting was transported to the University of Maryland Medical Center in Baltimore, Maryland, hospital spokesperson Lisa Clough said. There is no further information on the victim's condition or injuries.