The bomb squad Friday has finished its search inside Columbine High School in Littleton, Colo.
Officials say the squad recovered nearly 60 bombs from the school and the homes of the two gunmen, Eric Harris and Dylan Klebold.
Harris, 18, and Klebold, 17, stormed the school with bombs and guns April 20, killing 12 students and a teacher, and wounding 23 others before killing themselves.
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The sheriff's office has also finished investigating the crime scene, but federal agents remain on the campus. They're working on building three-dimensional models of each room to recreate the crime.
The school, which is closed, will remain a crime scene until the end of the month. Columbine students are completing this year's classes at neighboring Chatfield High.
Investigators were still trying to determine whether there was a third gunman, after some students told investigators of a third person shooting at students and launching bombs in the school.
In Wednesday's Denver Post, Sheriff John Stone said, "There was quite possibly one other person shooting. We do have witness statements."
CBS station KCNC in Denver reported Wednesday that at least 12 people have been identified by authorities to take lie detector tests in an attempt to help reveal if there was a third shooter.
|Mark Manes (AP)|
Meanwhile, Mark Manes, who was charged with selling an automatic handgun that was used in the bloodbath, was trying to work out a deal with prosecutors.
Manes' lawyer says his client practiced target-shooting with the two killers just weeks before the massacre, but did not know about their plans for the shootout. Some investigators have hinted that there could be more charges against Manes if ballistic tests show that any students were struck by bullets from the gun.