I think it was more the police got tunnel vision and became convinced of his guilt, so they did all they could to make sure it went down,
If you haven't already suggest you listen to the Undisclosed podcast season 2, a boy called Joey Watkins was convicted of murder but not only was there no evidence that he did it, there was evidence that he didn't do it. But the police were convinced he did it because he was a bad kid. The police got tunnel vision.