Malappuram district police sources said some steel pieces were found near the blast site and it is suspected that a 'pressure cooker' was used to trigger it.
He was arrested based on evidence police gathered during the process of investigation into the case.
The apex court set aside the order of the Kerala high court which had upheld the Central Administrative Tribunal's decision that had not found fault with the state government's decision to transfer Senkumar from the post of the state police chief.
