A US man who spent nearly 28 years behind bars for a murder he has always denied committing has had the conviction overturned in Missouri. Lamar Johnson, 50, walked out of the St Louis' courtroom a free man after a ruling by Judge David Mason on Tuesday. The judge said he acted after two witnesses had provided "clear and convincing evidence" that Johnson was innocent. He had been convicted of murdering Marcus Boyd in 1994. Johnson was visibly moved when the ruling was announced, while his supporters started cheering and applauding. "This is overwhelming," said Johnson, after leaving the courtroom. Last year, Attorney Kim Gardner had filed a motion seeking the release of Johnson after conducting an investigation together with the Innocence Project non-profit legal organization. Following Tuesday's hearing, Johnson's legal team criticized the office of the state attorney general which had pushed to keep him in prison. The office "never stopped claiming Lamar was guilty and was comfortable to have him languish and die in prison," Johnson's attorneys said in a statement. A spokesperson for the attorney general said in an email that the office would take no further action in the case. "Our office defended the rule of law and worked to uphold the original verdict that a jury of Johnson's peers deemed to be appropriate based on the facts presented at trial," the statement said. Marcus Boyd was shot dead by two masked men on Johnson's front porch in October 1994. Johnson has repeatedly said that he was not at home when the attack happened. Judge Mason issued his ruling after one witness had recanted his testimony, and an inmate had confessed that he shot Boyd with another suspect, Phil Campbell. During the initial trial, Campbell pleaded guilty to a reduced charge and was sentenced to seven years in prison. — BBC