The SIT sought extension of Mohanan's police custody following which Magistrate M Suhaib remanded him till July 11 for further investigation.
Chandrasekharan was murdered while returning home on his motorcycle at Vallikkode near Vatakara in Kozhikode district, with the issue raising a political storm in the state.
SIT's submission about senior CPI-M leaders' alleged involvement in the murder has brought more embarrassment to the party after its senior functionary M M Mani's controversial speech that the party in Idukki district in the 1980s drew up a list of rivals to be eliminated and killed three of them.
One more arrested for RMP leader's murder
Hate speech: CPI-M leader Mani appears for questioning
Cracks widen in communist ranks in Delhi
Chidambaram criticises Bengal govt, TMC hits back
SIT ready to probe any case raised by CPI-M