A Colorado judge has ruled that there is enough evidence for the man accused of killing 12 and wounding 58 others at a cinema last July to face trial.
The ruling follows a three-day hearing in which prosecutors laid out their case against the suspect, James Holmes.
It means Mr Holmes is set to be formally charged on Friday, although his lawyers have said he is not ready to enter a plea.
They have not explained their request for a delay in formal charges.
Earlier in the week, the court was told that Mr Holmes had laid incendiary booby traps in his apartment before the attack.
The mass shooting, which took place at the premiere of the new Batman film in Aurora, was one of the worst in US history.
During this week's hearing, defence lawyers called no witnesses and cross-examined only a few of those summoned by prosecutors.
While they have not indicated how Mr Holmes will plead, his lawyers have raised the issue of his sanity multiple times during the hearing.
Judge William Sylvester also ruled that the 25-year-old will still be held without bail on a total of 166 charges.