Police Narcotics Bureau (PNB) sleuths seized a stock of heroin with a street value of more than Rs 250 million from a house at Piliyandala on Thursday night.
The stock of heroin belonged to drug kingpin Wele Suda, who is in the Welikada Prison for heroin offences, police said.
It was the second largest heroin stock seized so far this year, police said, adding that they had also taken into custody an associate of Wele Suda along with two firearms in his possession.
The suspect divulged to police that he was running the heroin distribution business on the instructions of Wele Suda and he received the contraband from an unidentified person, who came in a van.
A chief peddler of Wele Suda contacted him daily and gave instructions on how to run the business, the suspect told police.
PNB officers said that they had information that Wele Suda was operating heroin cartels from behind bars using mobile phones. There was a network of peddlers who operated countrywide under instructions from Wele Suda.
The stock of heroin seized from Piliyanda weighed two kilos and 120 grams.