This would normally be the role of a forensic accountant.
My suspicion is that the Post Office wanted to do this "at scale" and "automate", and just assumed blindly their own records were accurate, because well... They must be!
Had they actually tried to investigate these as one by one offences, you'd gather evidence of individuals concerned making huge cash transactions to buy expensive cars and holidays. And when you didn't find any evidence of this unexplained enrichment (as there wasn't any), your investigator would point this out, and you'd realise you didn't have a case.
Similarly a photograph of the subpostmaster getting into their outright-owned Lamborghini would have been useful evidence there. The absence of any of the evidence of this enrichment seems absent throughout. Let alone the detailed forensic accounting to determine what was actually taken. I suspect the issue was they simply didn't have any way to tell what should have been there, other than what the defective horizon system said... They were trying to run at national scale, without enough ground truth information to validate their assumptions and detect the issue.
My suspicion is that the Post Office wanted to do this "at scale" and "automate", and just assumed blindly their own records were accurate, because well... They must be!
Had they actually tried to investigate these as one by one offences, you'd gather evidence of individuals concerned making huge cash transactions to buy expensive cars and holidays. And when you didn't find any evidence of this unexplained enrichment (as there wasn't any), your investigator would point this out, and you'd realise you didn't have a case.
Similarly a photograph of the subpostmaster getting into their outright-owned Lamborghini would have been useful evidence there. The absence of any of the evidence of this enrichment seems absent throughout. Let alone the detailed forensic accounting to determine what was actually taken. I suspect the issue was they simply didn't have any way to tell what should have been there, other than what the defective horizon system said... They were trying to run at national scale, without enough ground truth information to validate their assumptions and detect the issue.