I have personal knowledge of the pressures created during such serious investigations through having been involved in a murder case. Myself and another were identified as alibi witnesses by the defence. The murder had been committed many years previously. Both of us recalled the circumstances of the alleged alibi but neither of us could remember the date to closer than two or three months. Neither could we find documentary evidence of the alibi (which we both thought should have existed).
The police interviewed both of us several times, clearly concerned that we would suddenly remember something that would disrupt the prosecution. In the event, neither of us were called to court and the individual, who had been arrested during the commission of another very serious offence, was found guilty on other incontrovertible evidence.
My point is that the police (rightly) went to a lot of trouble to ensure that they were prosecuting the right man. In Steve Fulcher's case, it seems, his real crime was to do his job to the best of his ability instead of obeying rules which appear to have been created specifically to protect the guilty.