When Trea Ellinger left a Baltimore drug rehab facility last summer, he assured his anxious mother that everything was fine. He had his medications and was planning to meet up with his girlfriend.

By the following afternoon, he was dead — not from the violence his mom feared he might face, but because he didn’t survive an encounter with first responders in downtown Baltimore.

Ellinger, 29, died after being sedated and restrained. Despite repeated comments from police and medics at the scene acknowledging the dangers of lying face down in the prone position, responders failed to act urgently when the handcuffed Ellinger turned onto his stomach and remained that way for several minutes, according to investigators and experts.