The Colorado Department of Corrections has confirmed that an inmate assaulted theater shooter James Holmes and a security officer in the highest security prison in the state.

Holmes was not injured, officials say.

Mark “Slim” Daniels, 27, will be charged with assault on a correctional officer and an assault on Holmes, said Adrienne Jacobson, spokeswoman for the Colorado Department of Corrections.

“Daniels and Holmes are both housed at CSP. The incident occurred during an offender movement,” Jacobson said.

Daniels lunged at Holmes, took a few swings at him a few times.

“It was in passing,” Jacobson said.

Holmes was in a Management Control Unit, where he is allowed to spend four hours in a day hall. Currently there are no other inmates in his cellblock. The contact came as they were passing in a hallway.

The Denver Post learned of the assault Friday through a letter whose writer claimed to be Daniels. He said the assault happened on Oct 8.

The DOC has not seen a copy of the letter and therefore can’t say whether Daniels wrote it.

Holmes is serving life sentences in the murders of 12 people at the Century Aurora 16 theater. He also injured 70 people.

State corrections officials sent Holmes to the CSP, the highest security state prison in Colorado in September.

Daniels, who has used many aliases including Katrina Martinez, is serving time for numerous convictions out of Lakewood and Westminster and Adams County for menacing, auto theft, assault and smuggling contraband into prison.

He was charged with first degree assault on a guard in 2006.

Daniels is 6-feet-4 and weighs 195 pounds.

Kirk Mitchell: 303-954-1206, kmitchell@denverpost.com or @kirkmitchell or denverpost.com/coldcases