[gambiting]

>>considering what exactly is the likelihood of hundreds of postmasters simultaneously becoming thieves overnight

I mean, I don't think anyone assumed they suddenly and inexplicably became thieves, just that the fancy new software finally caught people who have been scamming the post office for years. Obviously the software was completely wrong and it's criminal what happened to those people.

[kristjankalm]

yes, this reasoning does make sense. but given the human cost it should only make sense if there's a significant prior: in most of these cases there was no previous evidence whatsoever, just a new system, and boom, thieves.

I think the core point here is how imbalanced this process was: postal system builds a new accounting program that shows money is missing. these people were convicted solely on the evidence that software said so, there was no burden on them to show that the money was actually missing. I mean, hard for me to grasp how is that possible. anyone can write a program that shows something. how is this sufficient proof to send people to prison? does it not need to touch some objective reality at some point?

[gambiting]

Yeah I mean if your brand new software discovered that a retail shop was suddenly missing £50k/month in income, surely you'd do full inventory to confirm £50k worth of goods is actually missing. No idea how you would do that in a post office, but I guess take an inventory of stamps and any other services sold?

[g_p]

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.

[_ea1k]

Wow, we should get raises for the fine job we are doing at keeping people from stealing from our agency!

[_ea1k]

I agree. My first thought on hearing this was that they'd look at the priors and realize there had to be a mistake.

My second thought was that most accounting departments I've worked with actually wouldn't do that, would blame fraud, and then would congratulate themselves at how much better they've gotten at detecting it!