Posted: Apr 06, 2021 4:04 PM ET | Last Updated: April 6 Minneapolis police Lt. Johnny Mercil, a use-of-force trainer, testifies during the murder trial of former police officer Derek Chauvin.(Court TV/The Associated Press) While neck restraints are part of the approved use-of-force training for Minneapolis police officers, Derek Chauvin's knee press into George Floyd's neck was a violation of policy, a lieutenant who trains officers in such techniques testified on Tuesday. Lt. Johnny Mercil, a Minneapolis police officer who trained Chauvin in proper use-of-force techniques, was shown a picture of Chauvin with his knee pressed into Floyd's neck during their fatal confrontation on May 25, 2020.