ROCHDALE, England — Shabir Ahmed, a delivery driver for two takeout places, did not have to go looking for young girls. Runaways and rebellious teenagers would show up at the restaurants, often hungry and cold. He slipped them free drinks and chicken tikka masala. “Call me Daddy,” he would say.

But soon, Mr. Ahmed, a father of four, would demand payback. In a room above one of the restaurants, according to testimony and evidence in later legal proceedings against him, he would play a pornographic DVD and pass around shots of vodka. Then, on a floor mattress with crumpled blue sheets and kitchen smells wafting from below, he raped them, and later forced them into sex with co-workers and friends, too.

The girls were too scared of him to talk. And when they did, no one believed them. Once, a 15-year-old got so drunk and upset that she smashed a glass counter. Mr. Ahmed and his colleagues did not hesitate to call the police. After she was released, she was coerced into sex four or five times a week, sometimes with half a dozen men at a time, in apartments and taxis around Rochdale, a town in northwest England near Manchester.

The police and other agencies were alerted more than 100 times over six years to the possibility that something very wrong was happening before Mr. Ahmed, now 61, was arrested and charged as the leader of a sexual exploitation ring that involved eight men of Pakistani descent and one Afghan. In May 2012, he was given a 19-year prison sentence for raping and abetting rape in a case involving at least 47 girls, all of them white.