Mahakanapathipillai, Public Relations Officer of the Sri Lankan Tamil cabinet minister Douglas Devananda, was shot dead in Wellawatte a residential area in south Colombo on Monday.
A spokesman of the Eelam Peoples' Democratic Party (EPDP) of which Devananda is the Secretary General, said that the party suspected the LTTE.
Mahakanapathipillai was earlier in the Eelam Revolutionary Organisation of Students (EROS), most of whose members are now with the LTTE.
The LTTE had earlier killed Balanataraja Iyer, another former EROS activist who was with Devananda as his ideologue and propagandist.
Balanataraja Iyer alias Sinna Bala, had been warned by the LTTE to lay off, before he was gunned down in Colombo.