Boston police have not revealed any suspects following the two explosions that happened around 2:50 p.m. Monday near the finish line of the Boston Marathon.
A scheduled 7 p.m. press conference was delayed until later in the evening to allow FBI agents to participate alongside Boston police.
At a press conference just before 6 p.m., Boston Police Commissioner Ed Davis denied early press reports that there was a suspect in custody. "There is no suspect in custody," Davis said, "we are questioning many people."
Davis refused to provide an update on the number of people who died as a result of the explosions.
The first blast sounded like a cannon firing, according to witnesses, and was followed by a plume of smoke several stories high. Screams from spectators were interrupted several seconds later by a second blast 50 to 100 yards away.
Fox News reports that Boston police are guarding a "person of interest" at a local hospital. "The person, who sources said was 20 years old, had severe burns, but authorities had not determined whether the person was a victim or a perpetrator," Fox News reported online and on air.
As of 8 p.m. Monday, there are two people reported to have died and around one hundred people reported injured, although the precise number varies among news outlets. When pressed on whether the number of dead had increased, Davis would only concede during the 6 p.m. press conference that "there are people who have expired."
"We are methodically going through the area" around the explosions, Davis said, searching for any other bomb materials.
The police chief clarified that a previous statement given to the press describing a fire at the John F. Kennedy Presidential Library as a third explosion was inaccurate.
"We will get to the bottom of this. We will find out who did this and we will find out why," President Barack Obama said at a White House press briefing. "They will feel the full weight of justice."
27,000 runners competed in the annual race and thousands of spectators were watching from along the route. Around 5,000 runners had not crossed the line at the time of the explosions, Fox News reports.
"Somebody's leg flew by my head," a spectator told the Boston Herald. "I gave my belt to stop the blood." The Herald reports that two children are hospitalized with lower leg injuries.