The man accused of opening fire in a Colorado cinema and killing 12 Batman fans last summer (12) has pleaded guilty to first-degree murder in a bid to avoid the death penalty.

Attorneys for James Holmes made the offer to prosecutors in a court filing on Wednesday (27Mar13).

Holmes, 25, has been behind bars ever since the massacre at the Aurora cinema last July (12) just before a screening of The Dark Knight Rises.

The filing reads: "Mr. Holmes is currently willing to resolve the case to bring the proceedings to a speedy and definite conclusion."

Earlier this month (12Mar13), a judge entered a not guilty plea on Holmes' behalf, but stated he could enter a plea of not guilty by reason of insanity at a later date.