This is a horrible euphemism picked up by Mark Peters in this article.
sudden in-custody death syndrome
I still want to believe this term is a piece of spectacularly dark humor, a Colbertian satire of medical truthiness, but alas, it appears to be real. I spied it in an article by Chris Thompson, who describes this "Orwellian euphemism" as the label for this situation: "...a suspect is intoxicated, usually on cocaine, he's already highly agitated and got his heart pumping like a marathoner, and the cops hit him with electricity or pepper spray, then pin him to the ground and shackle him. Not everyone dies after such an experience, of course, but an alarming number of them have." I don't know what's the sickest thing about this term: the resemblance to sudden infant death syndrome, or the fact that it reduces officer-caused deaths to "Wow, how'd that happen?" Excuse me while I shower—I need to scrub my psyche free of this term.
I've just finished reading Margaret Atwood's The Year of the Flood. If you haven't read it, it's a continuation of the story in Oryx and Crake, a near-future dystopian tale. Sudden in-custody death syndrome would fit snugly as a normal occurrence among the poor and oppressed in The Year of the Flood.