Announcing the decision at a press meet here, state home minister Ramesh Chennithala said a notification in this regard would be issued soon.
Describing the murder as a heinous crime, Chennithala said the decision was taken based on the state DGP's recommendation which stated that the case has a wider conspiracy angle.
Chief minister Oommen Chandy had in a letter yesterday informed Union home minister Rajnath Singh that all accused in the murder have been arrested and produced before a court.
On September 2, Singh had a telephonic conversation with Chandy and had expressed concern over the killings of political and social activists in the state.
The home minister had asked Chandy to take strict action to stop such political killings.
Quoting the DGP's report, Chennithala said the culprits' foreign and outside the state connection also could not ruled out.
The state BJP leaders had submitted a memorandum to chief minister Oommen Chandy seeking a CBI probe into the murder.
Manoj, a district functionary of the RSS, was hacked to death by an unidentified gang on September 1. The killing shocked the Sangh outfits as it happened on a day when BJP president Amit Shah was in Thiruvanathapuram.
RSS-BJP leaders alleged that the CPI(M) was behind the killing and gave a call for a dawn-to-dusk hartal in the state on September 2.
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