DENVER » Lawyers for Colorado theater shooting suspect James Holmes said today he would plead guilty and serve the rest of his life in prison to avoid the death penalty.

The offer comes just days before the prosecution was set to announce whether they would seek to have Holmes put to death for the attack that killed 12 people and injured 70.

Prosecutors wouldn’t say today whether they’d go along with a plea deal, and likely will consult with victims and their families before deciding whether to accept the offer.

If they agree, the case that started July 20 — when prosecutors say Holmes carried out the midnight massacre during a showing of the new Batman movie — could end quickly. In the filing, defense attorneys say the only thing that would hinder Holmes changing his plea on Monday is the prosecution’s decision.

In the filing, Holmes’ lawyers said they initially made the offer to plead guilty before Holmes’ arraignment on March 12. At that hearing, Holmes’ attorneys told a judge they weren’t ready to enter a plea in the case, and the judge entered a not guilty plea on his behalf.

Defense attorneys also said they’re still exploring a mental health defense and “counsel will vigorously present and argue any and all appropriate defenses at a trial or sentencing proceeding, as necessary.”

Prosecutors say Holmes planned the assault for months, casing the theater complex in Aurora, amassing a small arsenal and rigging potentially deadly booby-traps in his apartment.

Then he donned a police-style helmet and body armor, tossed a gas canister into the theater crowd and opened fire, prosecutors said.

Nearly eight months later, the defense has dropped hints about Holmes’ mental state but has given no clear statement on whether he would plead insanity.

Holmes, a former graduate student at the University of Colorado, Denver, had seen a psychiatrist at the school before the shootings.

Last week, his lawyers revealed that he was taken to a hospital psychiatric ward in November because he was considered a threat to himself. Holmes was held there for several days and spent much of the time in restraints.

The judge scheduled the trial to start Aug. 5, setting aside four weeks.