"...a five per cent error rate."
This is where Bayesian probability analysis is supposed to be used. In short, most randomly-selected people are not criminals. So false positives can easily dominate the findings unless the error rate is infinitesimal (which it isn't).
A root cause of all these AI and Machine Learning fiascos is that the people involved clearly don't understand the basics. Thus, their Confidence/Competence Ratio dangerously exceeds unity, and that leads to these sorts of fiascos. They need better managers to rein in the foolish expectations.
El Reg assists society by exposing such failures. Thank you.