US prosecutors rebuffed a reported offer by Colorado theater massacre suspect James Holmes to plead guilty in exchange for escaping the death penalty, legal documents showed.

A prosecutors' filing cited by the Denver Post and other media was scathing about a defense motion Wednesday which suggested a guilty plea in return for a sentence of life behind bars with no parole option.

"There is not -- and has never been -- an actual or unqualified 'offer' to plead guilty," prosecutors wrote, saying they are "extremely unlikely" to accept an offer unless they get more details from Holmes and his lawyers.

They want "specific access to information that would allow them to fully assess the defendant and his alleged acts for purposes of determining a just outcome to this case," the newspaper cited the filing as saying.

The 25-year-old is due in court Monday for a hearing at which prosecutors are expected to say whether they will seek the death penalty for the mass shooting, which left 12 people dead in July.

The defense motion filed Wednesday said Holmes "is currently willing to resolve the case to bring the proceedings to a speedy and definite conclusion for all involved."

"It appears the only impediment to a resolution of this case would be if the prosecution chooses to seek the death penalty," it said.

Holmes is accused over the July 20 massacre at a midnight screening of the Batman movie "The Dark Knight Rises" in Aurora, Colorado, which revived America's long-running debate about gun control.

Witnesses said Holmes threw smoke bomb-type devices before opening fire randomly with weapons, including an AR-15 military-style rifle, a 12-gauge shotgun and a .40-caliber pistol.

Earlier this month, a judge entered a plea of not guilty on behalf of Holmes and set an August date for him to stand trial over the horrific massacre. At that time, his lawyers said they were not yet ready to enter a plea.

When Holmes first appeared in court last year, he had bright orange hair and looked befuddled. He has since let his hair color grow out, and sported curly brown hair and a beard earlier this month.