VIDEO: Boston Marathon Bombing

Two explosions rocked the finish line of the Boston Marathon on Patriots' Day Monday afternoon, killing three and injuring 134 others including a police officer.

Police and fire personnel responded to the chaotic scene, following the explosions that were captured by several media outlets. The explosions occurred at about 2:50 p.m.

A 20-year-old Saudi Arabian suspect with severe burns is being guarded at a local hospital, according to the  New York Post .

President Obama said the federal government is mobilizing resources and the nation would "remember Boston in their prayers tonight," while speaking at a White House press conference.

"Make no mistake, we will get to the bottom of this," Obama said. "Any responsible individuals, any responsible groups will feel the full weight of justice."

Following the explosions, the  Boston Police Department  shut down cellular phone operation in the area to prevent detonation of other devices. At least five unexploded devices were located by police following the explosions, reports the Wall Street Journal .

The explosions occurred moments apart in front of Marathon Sports on Boylston Street, reports  CBS Boston . The bombs had been placed in trash cans near the finish line.

After he watched video of the bombings, law enforcement explosives expert David Spraggs told POLICE that high explosives were used with detonating velocities of between 15,000 and 26,000 feet per second. Spraggs, a certified bomb tech with the Boulder (Colo.) PD, guessed that each explosive device used 5-10 pounds of explosives.

"It was highly energetic," Spraggs said. "I don't think there's anybody out there who could say what it is right now. If I had to make a guess, I would say homemade explosives."

A Boston Police officer was among the wounded. He was wheeled from the scene at Copley Square with a leg injury. A Boston Globe sports producer captured street-level video of the explosions and the chaotic aftermath. NBC affiliate  WHDH  also has video.

A third explosion in the mechanical room of JFK Library in south Boston earlier in the day may be connected to the Copley Square bombings, Police Commissioner Ed Davis told the Boston Globe .

By Paul Clinton