Officers from the Peliyagoda crime division took Lasantha Premalal alias Kosgoda Rana and Sahan Silva, aka Meetiyagoda Raju, from a hotel in Ekala, Jaela.
A T-56 rifle, five bullets and a motorcycle were seized from them.
The suspects are being detained for 48 hours and under interrogation.
Among the killings they are responsible for is the gunning down of a man identified as Kosgoda Loku at Diyagoranduwa, Welipenna on May 08, police say.
The mastermind of these murders is said to be Kosgoda Suji, who is operating from a foreign country, due to his differences with Makandure Madhush, who is in hiding in Dubai.