Imaam Mohammed Imaath Fakir alleged to have encouraged the chief suspect of the Easter Sunday attacks, Zahran Hashmi has been detained by the police.
The imaam, who was detained in Dehiwala, has been to Syria and been a part of the ISIS terror group prior to returning to the country.
Nilan, another Sri Lankan who was a part of the ISIS, is stated to have been killed. Fakir is said to have returned to the island as an imaam and carried out ISIS information in Sri Lanka.
Police said the bulk of those detained have received training in Turkey. Three of the suspects arrested are also alleged to be suicide bombers.