i would say it s time to de-escalate force, sir. reporter: officer nicole mackenzie coordinates medical support services for the department. prosecutors using her to counter the defense argument chauvin wouldn t have known floyd was in distress because he was still talking. there is a possibility that somebody could be in respiratory distress and still be enabled to verbalize it. just because they re speaking doesn t mean they are breathing adequately. reporter: the defense team argues the crowd that gathered around the officers created a distraction and a threat. have you ever had to perform emergency services in a not even a hostile crowd, just a loud, excited crowd? yes. is that, in your experience, more or less difficult? it s incredibly difficult. does it make it more likely that you may miss signs that a patient is experiencing something? yes. reporter: nine minneapolis police witnesses have already testified against chauvin, including the department s chi