Demetrio Jackson was desperate for medical help when the paramedics arrived.The 43-year-old was surrounded by police who arrested him after responding to a trespassing call in a Wisconsin parking lot. Officers had shocked him with a Taser and pinned him as he pleaded that he couldn’t breathe. Now, he sat on the ground with hands cuffed behind his back and took in oxygen through a mask.Video above: Mother seeking justice for son’s deathThen, officers moved Jackson to his side so a medic could inject him with a potent knockout drug.”It’s just going to calm you down,” an officer assured Jackson. Within minutes, Jackson’s heart stopped. He never regained consciousness and died two weeks later.Jackson’s 2021 death illustrates an often-hidden way fatal U.S. police encounters end: not with the firing of an officer’s gun but with the silent use of a medical syringe.The practice of giving sedatives to people detained by …