Authorities released nearly 1,000 pages of new documents from the Columbine High School massacre Thursday, including step-by-step plans written by the two killers as they gleefully plotted the deadliest school shooting in US history.

Columbine High School students Eric Harris, left, and Dylan Klebold, involved in the killings of 12 students and a teacher at the school, are shown in this file image made from video released by the Jefferson County Sheriff's department Thursday, Feb. 26, 2004. The video was made as part of a school project at Columbine High School, in Littleton, Colo.. by Eric Harris and Dylan Klebold. This video was made prior to the killings at Columbine High School. [AP]

"Hell on Earth, ahh, my favorite," Dylan Klebold writes in the 1998 yearbook of Eric Harris above a drawing of a gun-wielding headless soldier. "So many people need to die."

The documents released by the Jefferson County sheriff include essays, school work and computer files from Harris and Klebold, the two suicidal killers. The papers also included a journal kept by Harris' father that refers to his son's disciplinary and psychological problems but sheds no light on whether he knew the teen might be capable of the slaughter that left 13 people dead.

A scrawled entry in Klebold's day planner apparently sketches out April 20, 1999, down to the minute, starting with a 6 a.m. meeting, a 10:30 a.m. "set up," an 11:12 a.m. "gear up" and at 11:16 a.m., "HAHAHA."

"Have fun!" Klebold writes in another notebook.

More than 20,000 documents and videos have been released since the attack, and some of the details released Thursday had been previously disclosed. Some documents include blacked-out portions, including song lyrics, names and computer logons. Sheriff Ted Mink also refused to release videotapes made by the gunmen, concerned they would encourage copycat attacks.

But the new material offered chilling details about the killers' activities in the months before the attack. They had "to do" lists, with each purchase of gasoline or a weapon marked off, and they had a hit list with at least 42 entries, all of them blacked out.

On a calendar entry for April 20, the time 11:10 is at the top, an approximate reference to the time the attack began. Elsewhere in the calendar are notations including "get nails" and "get propane, fill my clips" and "finish fuses."

"Once I finally start my killing, keep this in mind, there are probably about 100 people max in the school alone who I don't want to die, the rest MUST (expletive) DIE!" Harris writes in a journal entry from October 1998, six months before the attack.

The pages are filled with profanity, racial slurs and drawings depicting violence or death. Much of the Klebold material is handwritten, with detailed drawings of guns, sketches of what appears to be the Columbine cafeteria and his hopes for "500+" dead.

The material also includes a journal kept by Harris' father, Wayne Harris, with entries addressing threats made by his son against classmate Brooks Brown more than a year before the attack. The Brown family reported the threats in early 1998 and still contends the authorities or the Harrises should have taken action against the boy.

Wayne Harris writes in his journal about "idle threats of physical harm, property damage, overreaction to minor incidents," although the context of the notes is not clear. His attorney did not return a call seeking comment.

"We feel victimized," he writes. "We don't want to be accused every time something happens. Eric is not of fault. Brooks Brown is out to get Eric. Brooks had problems. ... manipulative con artist."

Brooks Brown said Thursday that Eric Harris had "lied about everything to his father and made him believe he was innocent and everyone else was the evil party."

Brooks' father, Randy Brown, said the sheriff's office should release everything, including the videos and audiotapes from the killers.

"There are lessons to be learned," he said. "This information will be hidden forever. They are trading their cover-up for the lives of children in other schools."

Brian Rohrbough, whose son Daniel was among those slain, said he struck by the fact that Wayne Harris had kept a diary tracking his son's problems.

"It tells you this kid was dangerous," Rohrbough said. "The premise that these are families that didn't know what was going on in their homes is completely refuted by this journal. They used all the influence they could muster to keep their kids out of trouble."

The Denver Post sued to force the release of the 936 pages. The Colorado Supreme Court left the decision up to the sheriff's office, and the Harris and Klebold families did not challenge the decision.