Boston Marathon Explosions Update: Only 2 devices found; FBI will investigate to "the ends of the earth"

(CBS) -- Deval Patrick, the governor of Massachusetts, told reporters Tuesday that "two and only two" explosive devices were found on Monday. Patrick said Bostonians should expect to see "continued heightened police presence" as the investigation continues  into the bombing that killed 3 and injured 176 people near the finish line of the Boston Marathon.

PICTURES: Explosions near Boston Marathon finish line

At the press conference Tuesday morning, Boston Police Commissioner Ed Davis said his department was "in the process of securing and processing the most complex crime scene we've dealt with in the history of our department." He said he expected that process to take two days and announced that the scene had shrunk from 15 blocks to 12.

Rick DesLauriers, the FBI Special Agent in Charge, said the agency is "following up on a variety of leads" and called the investigation "very active."

"We will go to the ends of the earth" to find who did this, DesLauriers said.

Col. Timothy Alben of the Massachusetts State Police warned residents that they would see an "enhanced presence" from the Boston Police, the State Police and the National Guard in the days ahead.

More than one official stressed that law enforcement is seeking photos and video from the marathon, both of the bombing and of the minutes and hours before and after.

"Bring forward anything," said  Alben. "You might not think it's significant, but it might have some value to the investigation."

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