A Cole County jury deliberated just 70 minutes before finding Khiry Summers guilty of second-degree murder, first-degree robbery and armed criminal action.
The seven-man, five-woman jury convicted Summers, now 21, for his role in the April 22, 2012, robbery of marijuana that ended in the killing of Columbia drug dealer Keith Mosely.
Presiding Circuit Judge Patricia Joyce will sentence Summers at a later date.
Summers faces two possible life prison sentences - or from 10-30 years - on the murder and robbery charges, and at least three years on the armed criminal action complaint.
That's the same set of sentences Brandon Chase, now 30, faces when he's sentenced later this month for his June 19 conviction of the same three charges, in the same crime.
Tracy Session, now 26, already is serving a 20-year sentence after pleading guilty last Nov. 7 to the same three charges.
Session did not admit to firing the fatal shot, but prosecutors said in Summers' trial this week and Chase's trial last month that Session stepped inside the doorway of 1029-B Buena Vista St. and fired one shot that hit Mosely in the chest.
Mosely died several hours after the shooting.
Summers told Cole County Prosecutor Mark Richardson Tuesday afternoon that he had "heard later" Session had fired the fatal shot, but denied being at the Buena Vista Street apartment at the time.
He testified he had gone to the Buena Vista apartment, just up the hill, because he had wanted to buy some marijuana.
But, Summers testified, he waited outside the apartment until he heard arguing, then he stepped just inside the apartment door and fired three shots "to startle them, to separate them so we could get out of there."
He denied being part of - or knowing about - any plan to rob Mosely of the drugs.
After firing those three shots, Summers testified he ran back to his fiancee's apartment because he was scared.
Boone County Public Defender David Wallis, representing Summers, reminded jurors that running isn't a crime, nor is buying marijuana.
But, Richardson noted during his closing arguments, others said Summers still was at the Buena Vista apartment when Mosely was shot.
Summers testified others in his family had hired Jefferson City lawyer Tina Crow Halcomb to represent him.
When he met with Halcomb May 2 - 10 days after the shooting - he said: "She gave me a statement to say" that was different from what he told the jury Tuesday.
And the story he told JCPD Detective Mark Edwards was different from what he'd told Halcomb, Summers said.
"Did she advise you to say what you told Edwards?" Richardson asked.
"No, sir," Summers told him. "I heard that on the street."
Richardson called Halcomb as a rebuttal witness.
"I know I didn't tell him to lie to police," Halcomb testified. "He knew what the truth was.
"He knew what happened that night."
She told Wallis: "There were several times that things Mr. Summers said (to Edwards) that he had had not shared with me."
After beginning their deliberations, the jury asked to review some exhibits - photographs taken inside the apartment and the video recording of Summers' May 2, 2012, interview with Edwards.
For about 90 minutes Tuesday morning, the jury watched and listened to that recording, of Summers telling Edwards what happened before, during and after the robbery and shooting that left Mosely dead.
During the interview, Halcomb helped Summers answer some of Edwards' questions, reminding Summers of things he had told her after she was hired to represent him.
Halcomb was allowed to withdraw from the case last Nov. 7 - the same day Session pleaded guilty - after Summers rejected a plea deal.
In the recording, Summers told Edwards he took part in a robbery - a fact he denied during his testimony Tuesday.
He said he had his brother's gun. "But I know I only shot into the floor," Summers told the veteran detective.
In his testimony Tuesday, Summers said: "I never committed no robbery. I never had any marijuana.
"I would never lie under oath."
But Richardson questioned that in his closing argument, shortly before the jury took the case.
"Two ounces of drugs. That's what he took," Richardson said. "He took it from a dying man."
Earlier trial coverage: