Holmes appeared in court Thursday, where his lawyer told the judge in the case that the defense must review thousands of pages of evidence before a preliminary hearing can be held. That hearing currently is scheduled for November.
Prosecutors said they, too, could use more time to gather evidence.
Judge William Sylvester said he will decide later this month whether to delay the hearing until January. The hearing will consist of a public airing of evidence against Holmes.
The 24-year-old is charged with killing 12 people and injuring 58 others in the July 20 shooting in the Denver suburb of Aurora. He has yet to enter a plea.
Also Thursday, mediator Ken Feinberg begins meeting with shooting victims and their families as he decides how to distribute $5 million in charitable donations to them.