R L V Ramakrishnan, who began the fast at nearby Chalakudy yesterday, said a year had passed since his brother's death, but no case had been registered so far.
"We have waited for a year. If we do not get justice we will protest in front of the secretariat at Thiruvananthapuram," he said.
The late actor's sisters Shanta and Ammini said they wanted to know the circumstances leading to his death.
"He was looking after us," they said.
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The actor, who had essayed many roles in south Indian films, was found in serious condition at his farmhouse at nearby Chalakudy. He was rushed to hospital, but passed away.
While a lab at Kochi had found traces of chlorpyrifos, a toxic pesticide in his viscera sample, a Hyderabad lab had stated that traces of methyl alcohol were found in his blood.
He was being treated for a liver ailment at Amrita Institute of Medical Sciences at Kochi, where he breathed his last.