Stewart has admitted to shooting 11 people, killing eight of them, at the Pinelake Health and Rehabilitation Center in Carthage in 2009.
His defense lawyers said the 47-year-old was essentially sleepwalking at the time due to taking a combination of prescription drugs.
Prosecutors spent 13 days presenting witness testimony and physical evidence to make their case that Stewart knew what he was doing and was on a rampage looking for his estranged wife, who worked at the nursing home.
During closing arguments Thursday, both sides picked up one of the four shotguns used in the murder rampage and racked it several times right in front of the jury box - it is a clear and distinct sound that's made when a shotgun is pumped to chamber a round before it's fired.
Assistant District Attorney Tiffany Bartholomew told jurors the clicking of the shotgun was the last sound several of the victims - 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 - heard before being shot-to-death.
Bartholomew said that Stewart knew exactly what he was doing. She said the shooting started in the parking lot when Stewart shot up his wife's car and he paraded through the nursing home, reloading every three shots as he fired at the elderly patients at point-blank range.
However, defense attorney Jon Megerian said Ambien and other drugs in Stewart's system caused him to be in a zombie-like state of mind when he entered the nursing home.
Megerian said Stewart was depressed because his wife, Wanda Neal, had recently left him and he thought he was going to die from prostate cancer.
If convicted, Stewart could face the death penalty.