That is testable. Prison populations should look different in areas where a larger fraction of serious crimes are solved. (It is hardly likely that a large enough fraction of people in prison are innocent to influence TFA's gigantic results of 89+%!)

So Occam's razor seems to imply that something changes in the face for people with e.g. (lead) poisoning, brain defects leading to psychopathy/violent tendencies or something else?

It could alternatively be in the life style of criminals. Drug use or attitude to others? Someone that really prey on people might even have changed hormone levels, or something, as it might be an evolutionary strategy?

Or just body language, but not for face pictures of course. In Sweden, when a state security group hired people with police training, they didn't hire police that ever worked on the streets because it changes the body language in some way; they are recognized by criminals -- and vice versa. (This is old, I have no clue how it is today.)