The New Haven police started surveillance in September, following tips from local residents: over a dozen drug dealers had set up shop in plain sight. The police were gathering evidence for a sting. They called it “Operation Green Sweep.”

Over the next three months, detectives collected oxycodone, heroin and crack cocaine, all in the shadow of City Hall. This month, police detectives obtained 16 arrest warrants, and last week, they moved in — to bust the drug market on the New Haven Green.

So far, police have arrested six of the 16 suspected dealers, but they are confident the drug market has collapsed. Police said they had hoped to eliminate the drug activity before the holiday season started drawing pedestrians to see the holiday tree on the Green.

As for catching the other suspects: “We’re working on it,” NHPD spokesman Joseph Avery said. “We expect to pick them up in dribs and drabs.”

The investigation is an example of New Haven Police Chief James Lewis’ new policing strategy, which he said involves police cracking down on drug trade in public areas.

Over the last few months, groups of “transient and indigent people” staked out benches on the Green throughout the day, Avery said Monday. But these people were not looking for places to rest.. Avery said the people served as middlemen, who carried small baggies of drugs to furtively sell to customers. According to criminal records, these salesmen were former robbers, burglars and con men.

By the time police descended on the Green, they all but knew the drug market on Yale’s doorstep was thriving. In addition to crack and heroin, undercover cops purchased Xanax, Percocet and methadone.

But Avery said detectives were confident that the market is now dead..

The bust on the Green is a recent example of the progress the narcotics unit has had since its recreation last fall. Mayor John DeStefano Jr. disbanded the narcotics unit after federal agents arrested the unit’s former head, Lt. William White, in 2007 for taking bribes and embezzling money from crime scenes. White was later sentenced to 38 months in federal prison.

The new unit, headed by Lt. John Velleca, seized in its first 100 days over two kilos of crack cocaine and $170,000 in cash, an amount Velleca has called “unprecedented.” Lewis said narcotics arrests have continued to increase this year compared to previous years.

Lewis said in a recent interview that he has made investigations like the bust on the Green a central focus of his police strategy, called “Targeted Activity Policing.” He said police will bring in the narcotics unit when a neighborhood has experienced high levels of crime or violence and when police know that the perpetrators are active in the drug trade. By arresting those criminals on drug charges, he said, police can give residents “a chance to take back their streets.”

“Our explicit goal is not to completely eradicate [drugs], though that would be nice,” he said. “The goal is to ensure security for the community, to prevent the disorder that causes crime and to send a message to the community that we care about them.”

Lewis also credited the strategy for the roughly 10 percent drop in crime the city has so far experienced this year.