Onlookers grew increasingly angry as they begged Minneapolis Officer Derek Chauvin to take his knee off George Floyd’s neck, but Chauvin would not let up, and another officer forced back members of the crowd who tried to intervene, witnesses testified Tuesday at Chauvin’s murder trial. Witness after witness described how Chauvin was unmoved by their pleas, with the teenager who shot the harrowing video of the arrest that set off nationwide protests testifying that the officer gave the crowd a “cold” and “heartless” stare. Chauvin continued to kneel on Floyd while fellow Officer Tou Thao held the crowd of about 15 back, even when one of the onlookers identified herself as a firefighter and pleaded repeatedly to check Floyd’s pulse, according to witnesses and bystander video. Earlier Tuesday, Donald Williams, one of the onlookers, testified that he called 911 after paramedics took Floyd away, “because I believed I witnessed a murder.” In a recording of the emergency call, Williams could be overheard yelling at the officers: “Y’all is murderers, bro!”