Investigators of the Columbine High School shooting case in Littleton, Colo., are scanning eMail messages and computer files of students who knew gunmen Eric Harris and Dylan Klebold to determine if any of them aided or knew of their plot.

Many of the students have voluntarily turned over their home computers to Jefferson County sheriff’s officials, Lt. John Kiekbusch said. Search warrants have been issued to America Online and other internet service providers, he said, and some school district computers also are being searched.

The investigation has focused on about 12 students who claim to be members of the “Trench Coat Mafia,” the clique to which Klebold and Harris belonged. Detectives are trying to find out if anyone visited Harris’ page on the internet, where he wrote about bomb-building and committing mass murder.

They also are looking for eMails that might have been sent to or from the teenage gunmen in the days before the April 20 attack that killed 13 and injured 21 before Klebold and Harris committed suicide.