The witness was allegedly suffering from advanced glaucoma at the time of the crime, severely limiting visibility. Surveillance video from the scene also revealed the eyewitness was much farther away than he initially claimed to be, according to the Exoneration Project.
The article says that the witness said that he was much closer than the cameras on site showed he actually was.
Also in the article, there’s the issue that CPD told others to identify Harris or else. One of them already recanted their statements.