They said the identities of the seven persons have been established and a search was on to nab them.
The police has also recovered the car used by the assailants from a house at Ramanthali area in the city.
RSS worker Choorakad Biju was hacked to death allegedly by CPI(M) activists at Payyanur town in Kannur district that has witnessed a series of clashes between the ruling CPI(M) and the RSS for the past one year.
Meanwhile, BJP state General Secretary Shoba Surendran said the state Governor P Sathasivam should quit if he is 'afraid' of Chief Minister Pinarayi Vijayan.
More From This Section
Speaking at a protest meeting in front of Kerala House at New Delhi, she said if the governor has some respect to the post he holds, he should take action against the government.
Her outburst came a day after BJP'S state unit submitted amemorandum to the Governor, seeking action and to declare Kannur a disturbed area and to impose AFSPA (Armed Forces Special Powers Act) there to maintain law and order.
"The BJP's demand for imposing AFSPA has no justification. Insulting the governor publicly for not acting in tune with their demand has exposed the BJP's autocratic nature," he said.
Countering BJP's charge that CPI(M) had unleashed attacks on RSS-BJP workers, Balakrishnan said 12 party workers were killed and 500 party cadres injured in assaults by RSS-BJP workers after the LDF government came to power in May 2016.
Balakrishnan also alleged that the saffron party had initiated a campaign to target the government under cover of the unfortunate incident of killing of Biju.