By Heather Knight
San Francisco Chronicle
SAN FRANCISCO — San Francisco police Sgt. Mark Obrochta cruises around the downtrodden Tenderloin in an unmarked car, listening on his radio to reports of drug deals going down within 1,000 feet of the neighborhood's three schools.
Two undercover officers - dressed in ratty cargo pants, sneakers and dirty T-shirts - wander the gritty streets. One of them tries to buy drugs, and the other watches from a half-block away and details into the radio his partner's attempts.
San Francisco police launch undercover drug stings