MINNEAPOLIS — The video of George Floyd gasping for breath was essentially Exhibit A as the former Minneapolis police officer who pressed his knee on the Black man’s neck went to trial Monday on charges of murder and manslaughter.Prosecutor Jerry Blackwell showed the jurors the recording at the earliest opportunity, during opening statements, after telling them the number to remember is 9 minutes, 29 seconds — the amount of time then-Officer Derek Chauvin had Floyd pinned to the pavement last May.The white officer “didn’t let up” even after a handcuffed Floyd said 27 times that he couldn’t breathe and went limp, Blackwell said in the case that triggered worldwide protests, scattered violence and national soul-searching over racial justice.“He put his knees upon his neck and his back, grinding and crushing him, until the very breath — no, ladies and gentlemen — until the very life was squeezed out of him,” the prosecutor said.Chauvin’s defense attorney, Eric Nelson, countered by telling jurors that “Derek Chauvin did exactly what he had been trained to do over his 19-year career.”Floyd was fighting efforts to put him in a squad car, Nelson said, as the crowd of onlookers around Chauvin and his fellow officers grew and became hostile.Speaking to the jury, the defense attorney disputed that Chauvin was to blame for Floyd’s death.