ST. LOUIS – A key witness whose testimony led to a conviction for a man accused of killing retired St. Louis Captain David Dorn in June 2020 had his own charges in the crime suspended in favor of probation.

On Wednesday, a jury convicted Stephan Cannon of first-degree murder, first-degree robbery, first-degree burglary, and three counts of armed criminal action. He is scheduled to be sentenced on the morning of September 13.

The very next day, prosecutors with the St. Louis Circuit Attorney’s Office and a city judge agreed to commute the sentence for Mark Jackson, who testified against Cannon during the three-day trial.

Jackson pleaded guilty on Thursday to first-degree robbery and first-degree burglary and received a 15-year suspended execution of sentence, with five years of probation. He was credited with time served and released.

“I think the sentence is fair and just. I hope he can turn his life around, like he says he wants to,” Ann Dorn, Capt. Dorn’s widow, said in court Thursday.

Jackson had also been charged with second-degree murder, stealing $750 or more, and three counts of armed criminal action. The state dropped those charges.

David Dorn died on June 2, 2020, while responding to a burglar alarm at a friend’s business, Lee’s Pawn and Jewelry. Looters broke into the store around 2 a.m. and Dorn was fatally wounded when he confronted them. He was 77.

Cannon and Jackson had been arrested days after Dorn’s murder.

A jury of nine women and three men began deliberations shortly after 12:35 p.m. Wednesday and returned its guilty verdict against Cannon just before 3:45 p.m.

Lead prosecutor Marvin Teer Jr., who had been called out of retirement by St. Louis Circuit Attorney Kim Garder, expressed gratitude that the Dorn family would get some closure in their lives. He’d been living in San Diego when he was asked to prosecute the case. The former judge and prosecutor said he hadn’t tried a case in 22 years. 

Gardner released the following statement Wednesday at the conclusion of the trial:

Based upon the cooperation from an outraged St. Louis community, a collaboration with the St. Louis Metropolitan Police Department and the City of St. Louis Circuit Attorney’s Office, charges were issued, and the case was taken to trial. Today a jury found Mr. Stephan Cannon guilty of first-degree murder … for the tragic death of former SLMPD Captain David Dorn.

While nothing can bring Captain Dorn back to his loved ones, Mr. Cannon has been held accountable for his crimes committed in the City of St. Louis, and justice has been served.

Kim Garder, St. Louis Circuit Attorney

Jackson testified Tuesday that he and Cannon had known one another for seven years and were friends at one time. On the evening of June 1, 2020, Jackson said he, Cannon, and a third person got into his Pontiac G6 and drove around town looking for places to loot amid rioting in the city.

Jackson said they looted some stores before going to Lee’s Pawn and Jewelry well after midnight on June 2. According to Jackson, Cannon was wearing a black Adidas tracksuit and white hat. Jackson claimed he was inside the pawn shop when Capt. Dorn arrived. He told the jury he hid inside the store when Dorn fired two shots into the air to disperse the crowd. He then heard more gunshots before Cannon came to the front of the store and called out that it was time to leave. 

Jackson told the court he did not see Dorn’s body and was unaware at the time Cannon had shot the retired captain. He spoke with Cannon next time via the Facebook Messenger app and said that’s when Cannon admitted to shooting Dorn.

He admitted to telling police several different stories to cover for Cannon but found himself charged with murder. Under cross-examination, the defense played eight different clips of Jackson’s interrogation for the jury, showing him attempting to lie or deflect detectives from their investigation.

Cannon’s defense attorney, Brian Horneyer, played clips of Jackson telling detectives, “You tell me what to say and I’ll say it,” and “I’ll witness whatever you want me to witness.” Jackson said he meant in terms of telling the truth.

Jackson admitted to signing a plea agreement approximately two months ago, but without any guarantee of a reduced sentence.

“My only expectation is to clear my name,” he said.

However, the defense pointed to pretrial testimony in which Jackson said he expected to get just two years for his cooperation.

In closing arguments, Horneyer said police and prosecutors realized they didn’t have a good case, so they went to Jackson, “who lies as easily as he breathes,” to testify against Cannon.

Horneyer said he will file an appeal on Cannon’s behalf. If that is denied at the time of sentencing, he plans to seek a retrial.