The door of the house and some part of the front portion suffered damage and glass splinters were seen strewn on the spot, police said.
District Superintendent of Police M Durai visited the house, now occupied by the family of Raja's brother, this morning and held an on-the-spot investigation into the incident that occurred around midnight last night.
The duo had come riding a two-wheeler and fled the spot after throwing the petrol bomb, the SP said, adding, CCTV recordings in the street showed a motorbike passing through it.
Police said they arrested 42 members of BJP and Hindu Munnani for staging a road block in the town demanding the arrest of those responsible for the attack.
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Armed Police picket had been posted at the house, police said.
Raja has received murder threats twice in the past two years. In 2013, a two-member gang had gone to a garden owned by Raja and threatened the security and told him that they would kill Raja.
Last year, two persons had dropped a letter threatening that Raja would be murdered in the house.