The offer sets up a possible end to the case if prosecutors agree to a plea deal. They're set to announce Monday whether they'll seek capital punishment and wouldn't comment Wednesday on the filing, although defense attorneys said their offer hasn't been accepted.
"The prosecution at this time has not accepted that offer because it may choose to pursue the death penalty. Consequently, it appears the only impediment to a resolution of this case would be if the prosecution chooses to seek the death penalty. If the prosecution elects not to pursue the death penalty, it is Mr. Holmes' position that this case could be resolved April 1," defense lawyers wrote.
Prosecutors would likely consult with victims and their families before deciding whether to accept the offer. Holmes' lawyers said the case could end Monday if prosecutors accept.
Holmes' attorneys told a judge earlier this month they weren't ready to enter a plea in the case, and the judge entered a not guilty plea on his behalf.
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.