The estate figures in the disproportionate assets case involving jailed AIADMK general secretary V K Sasikala and Jayalalithaa, among others.
The trio - Satishan from Pudukkad, Shibu from Kodakara and Santosh from Vellakulangara near Thrissur, were taken into custody based on CCTV footage and their stay at a cottage in Kothagiri a day before the murder on April 24, police said.
They said the CCTV footage shows the trio moving in a car in the area.
Police had questioned a guard who escaped the attack for the second day yesterday.
A 10-member masked gang was suspected to have carried out the attack. A door of the bungalow was broken open and some suitcases found open, leading to suspicion that the gang wanted to steal valuables and documents.