They said searches have been intensified to nab the trio and teams despatched to various states.
The Special Investigation Team (SIT) probing the case has already filed chargesheet against the three persons and were on the lookout for three others.
A powerful five feet pipe bomb planted under a culvert was recovered minutes before Advani, on a nationwide anti-corruption yatra in October 2011, was to cross the culvert at Alampatti near Tirumangalam. The bomb was defused later and Advani was directed through a different route.
A special investigation team of CB-CID investigated the case and arrested three persons. The team is on the lookout for three others. They had registered a case under Explosives Act and IPC Sections 120 (conspiracy) and 307 (attempt to murder).