They are only applying to people known to police.

For anyone known to police who has killed twice already, you don't need any fancy algorithm: just short-circuit to "highly likely". They tried killing once, and it suited them well enough to do it again. People known to police only for petty or non-violent crimes like shoplifting or possession of dope can probably be filtered out. You need the algorithm for everything in between.

Then do what? Arrest them? Put a camera on their head? The UK police state is stronger than ever.