evidence: Los Angeles Police Department Sgt. Jody Stiger, a use-of-force expert who testified for the prosecution in Derek Chauvin's murder trial, agrees with Minneapolis Police Chief Medaria Arradondo that the defendant violated his department's policies when he pinned George Floyd to the pavement with his knee for more than nine minutes. Stiger, who testified yesterday and today, elaborated on the reasoning behind that conclusion. [...] Stiger said kneeling on Floyd for as long as Chauvin did amounted to deadly force, because "the pressure that was being caused by the body weight could cause positional asphyxia." He said the danger of positional asphyxia, which has been widely recognized for decades, exists whenever a handcuffed arrestee is restrained on his stomach for an extended period of time. He noted that applying pressure magnifies that risk. [...] When prosecutor Steve Schleicher asked Stiger to clarify whether the risk of positional asphyxia depends on whether pressure is applied specifically to the neck, Stiger said "it's the pressure on the body" that "complicates breathing." Whether Chauvin's knee was on Floyd's neck or, as Nelson prefers to describe it, "between the shoulder blades at the base of the neck," the crucial point is that he was pressing down on Floyd throughout the encounter, which aggravated the asphyxiation risk created by forcing him to lie on his chest with his hands behind his back. That situation made Floyd's complaints that he could not breathe perfectly understandable and plausible, even if the cops thought he was faking.