A mixed martial arts fighter who loudly urged former Minneapolis police officer Derek Chauvin to take his knee off George Floyd's neck testified Tuesday about how he called 911 during the incident, "because I believed I witnessed a murder." Prosecutor Matthew Frank played back Williams' 911 call, on which he can be heard telling the dispatcher that Chauvin had been keeping his knee on Floyd's neck despite warnings that Floyd's life was in danger, including an off-duty firefighter who urged the officers on the scene to check his pulse. She offered to switch him to a sergeant. As he's being switched, Williams can he heard yelling at the officers, "Y'all is murderers, bro." Frank noted that the call terminated abruptly. Williams said he didn't remember for sure why he hung up, but said that he might have felt intimidated by officer Thao, the officer who can be seen on the Facebook video holding back the crowd. Williams could be seen on the video feed wiping his eyes with a tissue after giving that account. Williams was testifying for the second day in Chauvin's trial. He described how he say Floyd "going through tremendous pain," grunting, with his eyes rolling back, drooling and gasping for air while he was under Chauvin's knee. He said he shouted at the officers because he had trained alongside law enforcement officers at his mixed martial arts gym, so he felt the need to speak up, but got no response to his concerns. Subscribe to our YouTube channel: https://bit.ly/2TwO8Gm Bloomberg Quicktake brings you live global news and original shows spanning business, technology, politics and culture. Make sense of the stories changing your business and your world. To watch complete coverage on Bloomberg Quicktake 24/7, visit http://www.bloomberg.com/qt/live, or watch on Apple TV, Roku, Samsung Smart TV, Fire TV and Android TV on the Bloomberg app. Have a story to tell? Fill out this survey for a chance to have it featured on Bloomberg Quicktake: https://cor.us/surveys/27AF30 Connect with us on… YouTube: https://www.youtube.com/user/Bloomberg Breaking News on YouTube: https://www.youtube.com/c/BloombergQuickTakeNews Twitter: https://twitter.com/quicktake Facebook: https://www.facebook.com/quicktake Instagram: https://www.instagram.com/quicktake