The legal advise was given after the state had sought the DGP's opinion on a CBI probe into the conspiracy charge of the murder.
Earlier, the Chombal police station in kozhikode had registered a case relating to the conspiracy charge of the murder case and filed a chargesheet before the court.
The committal proceedings relating to the case is pending before a magistrate court in Kozhikode district.
RMP and Chandrasekharan's widow, Rema, has also sought a CBI probe into the killing and has threatened to go on fast, demanding the same.
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Chandrasekharan, a former CPI(M) worker from the red bastion Onjiyam near Vatakara in north Kerala, was hacked to death by an eight-member gang on May 4, 2012.
He left CPI(M) a few years ago over differences with the leadership and floated a parallel outfit, the RMP.He was 51 at the time of murder and suffered 51 hack injuries on the body.