Thamindu, who is said to be the main financial controller of underworld leader Dematagoda Chaminda, was arrested with Rs 1.5 million and 5g of heroin worth Rs 125,000 by the Walana Anti Vice Squad yesterday at Narahenpita.
Thamindu is said to be in possession of a 168-page book, which details how the revenue, earned through Chaminda's drug business, should be distributed.
A top Police officer involved in the investigations told that the book contained the official ranks of several Prisons Department officers.
Police investigations had also revealed that following the arrest of Dematagoda Chaminda last November, Thamindu had been entrusted with the task of managing the drug trade.
Police added that 84 pages of the book are in code.