Prosecutors will seek the death penalty against accused theatre gunman James Holmes in the slaying of 12 moviegoers during a showing of the Batman film The Dark Knight Rises last year, the district attorney said in court yesterday.

Holmes, 25, is accused of opening fire inside a suburban Denver theatre during a midnight screening of the movie last July in what was one of the deadliest outbursts of gun violence in US history.

Holmes is charged with multiple counts of murder and attempted murder in the shooting rampage, which also wounded 58 moviegoers. Another dozen people suffered non-gunshot injuries as they fled the Aurora, Colorado, cinema.

Arapahoe County District Attorney George Brauchler had previously announced he had assigned a death penalty lawyer to the prosecution team, and in court documents released March 28 rejected a defence offer to let Holmes plead guilty and serve a life sentence if capital punishment were taken off the table.

Arapahoe County District Judge William Sylvester entered a not guilty plea for Holmes last month but said he would consider allowing that to be changed to not guilty by reason of insanity.

Last week, public defenders said in a court filing that Holmes was willing to plead guilty and serve a life sentence without the possibility of parole if prosecutors agreed not to seek to have their client executed.

While Holmes’ attorneys said they are prepared to mount an insanity defence, they wrote in the filing that “Mr Holmes is currently willing to resolve the case to bring the proceedings to a speedy and definite conclusion for all involved.”