I base my belief in them on public backlash...
Whenever there is a high profile, emotionally charged case, LE *know* they are under a microscope. They have their superiors disecting every move and their evidence and investigative techniques are double, triple checked. While I like to believe that they do this for every case, I am a realist and know that these high profile cases are scrutinized beyond the norm.
Yes, if they got this one wrong, they're certainly going to have some explaining to do.
That said, in high profile cases, there is also pressure for an arrest, which can lead to errors.