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.

Then, 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 police has spread quietly across the nation over the last 15 years, built on questionable science and backed by police-aligned experts, an investigation led by The Associated Press has found. Based on thousands of pages of law enforcement and medical records and videos of dozens of incidents, the investigation shows how a strategy intended to reduce violence and save lives has resulted in some avoidable deaths.