James Holmes

More details have emerged about the attack on Aurora movie theater shooter James Holmes in a Colorado state penitentiary in October.

Holmes, 28, opened fire in a movie theater, killing 12 and injuring 70 in 2012. He was convicted and sentenced to life in prison without the possibility of parole in August.

Holmes was housed separately from the general population for his own safety. But prison officials said a guard left a security gate open just long enough for another inmate to slip through and attack Holmes.

The inmate, convicted car thief Mark “Slim” Daniels, slipped through the open gate and attacked Holmes.

“Offender Daniels began hitting offender Holmes, in and around his head, with his fist,” a corrections officer wrote in an incident report.

“Daniels kept swinging over the top of [one officer’s] head, still hitting offender Holmes.” Daniels “landed at least two blows to offender Holmes before I was able to get behind” him.

As other officers rushed over, Daniels accidentally punched a female staffer “on the left side of her face below the eye and on the top of her head,” according to the report.

In a letter to a Colorado newspaper in December, Daniels expressed regret at not killing Holmes and sending him “packing to Satan’s lake of fire.”

Daniels wrote: “It was just impossible to do by myself with so many cops. I did get him six or seven good ones… He was very scared.”

As a result of his notoriety, Daniels received cash and gifts from the public. His prison commissary holds $75 (the maximum allowed) and his mother quickly established a GoFundMe account to raise funds to help pay for bills she claims is associated with the attack on Holmes.

Calling the attack “a minor incident,” prison officials secretly transferred Holmes out of state to an undisclosed prison.

The unusual move resulted in sharp criticism from critics who can’t locate Holmes in the prison system.

When asked about Holmes’ location, Corrections Department spokeswoman Adrienne Jacobson at first said his location was “public record.”

But when told his name doesn’t come up in any public records search, she refused to answer, then she said an agreement with other prisons regarding interstate transfer of prisoners “requires confidentiality.”

District Attorney George Brauchler, who prosecuted Holmes, said he is concerned that the state is hiding Holmes.

“This guy should be serving a sentence in Colorado. And if not, we should know why and where he is,” Brauchler told ABC News.

Colorado Prisons Director Steve Hager defended Holmes’ transfer, saying: “the attack was part of the reason for moving him. There were many concerns; the attack was part of the concern.”

Hagar said Holmes had been the only inmate confined to the prison’s Management Control Unit. He said prison officials were trying to figure out what to do with him when the attack occurred.

“At that time, they were trying to find the best placement for him,” Hager said.

Hagar told ABC News that prison officials were reviewing the closed circuit video to determine exactly what happened the day of the attack on Holmes.

But when ABC News requested a copy of the video, the state’s assistant attorney general, James Quinn said, “there are no stills and no video.”