Edward Earl Johnson, convicted by the Mississippi, U.S. for the murder of a policeman, and the sexual assault of an old woman was executed on May 20, 1987 . Throughout his eight years on death row he continued to plead his innocence. In the months after the execution, a book claimed that the key witness was unreliable, changing her story and identification of her assailant several times at the time of the event and in subsequent questioning.
Another woman who wanted to testify that Edward was with her when those crime happened was prevented from appearing in court by cops.
Here’s the documentary about the case.