Late last year, as a team of Minnesota state prosecutors was preparing for the trial that would ultimately convict former Minneapolis police officer Derek Chauvin of murdering George Floyd, they received a series of videos depicting Chauvin’s handling of another case three years earlier that by their own description shocked them. The videos, from Sept. 4, 2017, allegedly showed Chauvin striking a Black teenager in the head so hard that the boy needed stitches, then allegedly holding the boy down with his knee for nearly 17 minutes, and allegedly ignoring complaints from the boy that he couldn’t breathe.