Scott Ostrem was ordered to undergo a mental health evaluation in January. A preliminary hearing was set for June 8.
Dave Young, the 17th Judicial District attorney, said the ruling puts the case "back on track."
Ostrem is facing six counts of first-degree murder, and 30 counts of attempted first-degree murder and one count of crime of violence for the Nov. 1 shooting.
Ostrem walked off his job one morning and then went into the Walmart and opened fire near the checkout area at the front of the store.
Ostrem was identified as the shooter by security video.
The next morning, law enforcement spotted his red vehicle near his home near West 72nd Avenue and Pecos Street.
After a brief chase, he was taken into custody and booked into the Adams County Detention Center.
Ostrem has had a history of run-ins with law enforcement and his neighbors.
A stepsister said Ostrem allegedly heard voices in his head after using LSD years ago.