ABC News: Inside the prison assault on Aurora theater shooter James Holmes

Colorado movie theater shooter James Holmes was not supposed to interact with other prisoners, but after a security gate was left open at just the wrong time, another inmate snatched an opportunity to attack the mass killer in the state penitentiary, even throwing punches as guards tried to pull the two apart, according to documents and a top prison official who spoke exclusively to ABC News.

Though officials insisted it was a minor incident, prison higher-ups said the episode proved Holmes was in so much jeopardy that he had to be secretly transferred out of state to an undisclosed location in what one critic called a highly unusual move.

“We had not allowed Holmes at that time to come into daily contact with other offenders,” Colorado Prisons Director Steve Hager said in an exclusive interview in February. “That was not part of the management plan of him.”

Hager explained that “the attack was part of the reason for moving him. There were many concerns; the attack was part of the concern.”

Documents obtained by ABC News show that Holmes, 28, was not supposed to cross paths with anyone but prison staff while housed in the Colorado State Penitentiary in Canon City. But as Holmes exited the office of his case manager on Oct. 8, a prison staffer opened a sliding gate without realizing he was putting Holmes in close proximity with another inmate, convicted car thief Mark “Slim” Daniels. The officer escorting Holmes was unable to radio the officer controlling the gate “as his battery had gone dead,” according to a so-called “intelligence assessment” drafted after the incident occurred.

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