The documents include messages that Eric Harris and Dylan Klebold wrote in each other's yearbooks, and a journal kept by Harris' father, Wayne Harris. Jefferson County Sheriff Ted Mink has said he will not release videotapes the gunmen made, for fear they would encourage copycat attacks.
Harris and Klebold killed 12 students and a teacher on April 20, 1999, before turning guns on themselves.
Mink said this month that he wanted to release 936 pages of documents but held off to give the parents time to object.
Gary Lozow, an attorney for Klebold's parents, said the Klebolds would not try to block the documents' release. Mink announced their release hours later.
It was not immediately clear whether Harris' parents had told the sheriff's department they would not fight the release. An attorney for Harris' parents did not immediately return phone calls.
"No one has filed any challenge to the sheriff's original decision," sheriff's spokeswoman Jacki Kelley said.
The Denver Post had sued to force release of the material, and the Colorado Supreme Court last year left the decision up to the sheriff.