Stewart was treated at a hospital for a gunshot wound before he was transferred to North Carolina's maximum security Central Prison in Raleigh. The warrants say he made the comment to a nurse.
He told the nurse that he had taken six "nerve pills" and did not remember anything else.
Investigators say Stewart went into the Pinelake Health and Rehab Center on March 29 and started shooting. Carthage police officer Justin Garner arrived just five minutes after the shooting started and stopped Stewart by shooting him in the upper body. Garner was wounded by three shotgun pellets to the lower leg.
Residents Tessie Garner, 75; Lillian Dunn, 89; Jesse Musser, 88; Bessie Hedrick, 78; John Goldston, 78; Margaret Johnson, 89; Louise DeKler, 98; and nurse Jerry Avant, 39; all died in the attack.
Investigators haven't given a motive, but Stewart's estranged wife was an employee at the nursing home. She hid in the bathroom of a locked Alzheimer's patient area and survived the attack.
The court documents say investigators went to Stewart's home after the attack and found ammunition on the kitchen table and a bed, eight guns, and an assortment of scopes and gun barrels.
The warrants also say they found unspecified pill bottles and several pieces of notebook paper with writing, but details of what was written haven't been released.
The warrants also allowed investigators to draw blood from Stewart "to determine if there is any controlled substance in his body."
Stewart is facing eight counts of first-degree murder.