A man serving more than 3,000 years in jail for the murders of 12 people in a cinema warned prison authorities he could kill again, according to newly released footage.

James Holmes walked into a showing of The Dark Knight Rises in Aurora, a suburb of Denver, Colorado, and opened fire in July 2012. The attack, which he carried out while listening to loud techno to drown out his victims’ screams, also left 70 people injured.

The jury at his subsequent trial dismissed his defence of mental illness, and he escaped the death penalty but was sentenced to 12 life sentences plus 3,318 years in jail.

US prosecutors have now released hours of video showing him talking about the massacre to William Reid, a court-appointed specialist who evaluated his sanity.

When asked if he was to pose a danger to anybody, he told the psychiatrist: “Well, if I killed somebody then there’s a likelihood that I would kill again.”

Mr Reid was also heard asking Holmes whether the prison authorities “should be worried about you”. He replied: “I’d say so, yeah.”

Holmes also revealed he did not have a plan for the aftermath of the murders.

Aurora massacre: Police officer describes suspect James Holmes as 'relaxed' and 'detached' in aftermath of killings Show all 2 1 /2 Aurora massacre: Police officer describes suspect James Holmes as 'relaxed' and 'detached' in aftermath of killings Aurora massacre: Police officer describes suspect James Holmes as 'relaxed' and 'detached' in aftermath of killings Colorado shooting suspect James Eagan Holmes Colorado shooting suspect James Eagan Holmes Reuters Aurora massacre: Police officer describes suspect James Holmes as 'relaxed' and 'detached' in aftermath of killings 27.reuters.jpg Relatives of victims at the hearing in Colorado yesterday REUTERS

He said he did not “whether to die or not or drive away or where I would go – I kind of left that all up to the spur of the moment.”

Holmes also said he felt uncomfortable being handcuffed when found by police officers, but otherwise had no feelings about his arrest.

“I didn’t have any feelings about it,” he said. “I just kinda felt it was something that was going be done … I didn’t have any feelings.”

Most of the 2014 videos were shown to the jury at Holmes’ trial.

Prosecutors’ spokeswoman Vikki Migoya said people who want to see the videos can contact Colorado’s 18th Judicial District Attorney’s Office for access to a website where they are posted.

The videos were released at the request of attorney Steven Zansberg, who said he was representing a documentary producer whom he declined to identify.

Jeff Roberts, president of the Colorado Freedom of Information Coalition, praised the decision to release the videos. “I think it goes to the public being able to understand what happened,” he told The Aurora Sentinel.