The accused were brought to the place of crime under tight security.
Nandu was allegedly killed by SDPI members after a clash erupted between two groups in Cherthala, Vayalar yesterday night.
An RSS shikshak was hacked to death at Nagamkulangara in Vayalar near Cherthala on Wednesday.
Though the reason behind the killing has not been ascertained yet, police suspected it could be a fallout of old enmity.
Roy was found hanging near his home in Hemtabad area of North Dinajpur district on July 13 last year.
The Youth League has suspended Irshand Kalloravi from the organisation after he was arrested for the murder of Abdul Rahman.
The CPM has alleged that RSS was behind the murder.
The BJP alleged that the Trinamool Congress was behind the incident, and called a 12-hour bandh in Tufanganj on Thursday.
Police data studied by this newspaper showed that of the 47 political killings involving BJP and TMC workers since the 2019 Lok Sabha elections, 38 happened in south Bengal.