From recaps of the last season.
"Dar tells Carrie that his group found Quinn when he was 16 in a foster home in Baltimore. "He was a natural from the start," he says."
"a boy found in a Baltimore foster home at 16, someone “real,” yet “pretty enough” to attract useful attention — has left us with an image of desperation, even exploitation, that brings to mind the trafficked teenagers holed up in the Russian not-so-safe house where Allison waits for transit out of Germany."
I think I was thinking of him being a killer, then, not something else.