St. Louis police detective Luther Hall was brutally beaten while working undercover at a protest against police brutality in September 2017. Now three fellow officers are on trial for the assault, which they claim was a case of mistaken identify. One of the officers already pleaded guilty and admitted to lying on the stand. Lauren Trager, an investigative reporter with CBS affiliate KMOV-TV, joins CBSN AM's Anne-Marie Green to discuss the case.
