When federal agents closed in on German Rios on April 21, 2011, at the Woods Island ­MBTA Station, they found a half kilogram of cocaine in his backpack, according to a police report. Rios was sentenced to seven years in prison for drug trafficking.

But Wednesday, he was back in court along with 19 other ­defendants before Suffolk Superior Court Judge Christine M. McEvoy, as part of a parade of drug cases connected to former state chemist Annie Dookhan.