Are black faces overrepresented or underrepresented? According to AI researchers, we're faced with Schrodinger's Mugshot--there's simultaneously too many and too few!
Without additional leads police are strongly incentivized to pick one of the results and run with it and in many cases with enough data you have enough to get a plea or conviction even if they didn't do it especially if the person so selected was in the database in the first place because they have a record.
Convictions/pleas are obtained all the time with similar levels of proof.
This is fundamentally the same problem as dragnet searches of phone GPS to see who was in a space in a range of time. It could be a valuable investigative tool but its also a great way to "solve" a crime by finding someone to pin it on.
You then deploy that model, and use the model to match black person detained by racist officers against a database of photos that the police have from before. In that database the majority of people are black.
Shitty AI that was not properly taught what black people look like because most of the people in the training data were white, says that it found a probable match for detained black person.
Racist officers do not attempt to second guess the computer, so they throw innocent black person into their car and drive off to the police station.