Those postmasters defending charges of theft against them in the 2000s should not have had to prove that the computer system they were forced to use had bugs. In order to prosecute them in the first place, the Post Office should have had to prove, beyond a shadow of a doubt and without risk of bias, that the computer system was correct. So, independent review at the very least, not testimony from parties with a vested interest in the outcome. This mess was as much a failure of the UK legal system as it was of the active efforts of the Post Office and Fujitsu to deceitfully protect their own interests above the postmasters affected.
It's like a murderer giving evidence against a random stranger and being believed at face value because they provided all the evidence first hand.
It's like a murderer giving evidence against a random stranger and being believed at face value because they provided all the evidence first hand.