Goa Police have circulated this letter to all the police stations in the state and handed over the case to the Anti Terrorist Squad (ATS).
The postcard threat letter was received at the State Secretariat last week following which Goa Police swung into action, a senior police official said today.
"All the agencies of state police are investigating this letter. We will soon be able to find the source of it," the police official said.
"ISIS was written at the bottom of the postcard," the official confirmed.
The letter has expressed anger over ban on cow slaughter in the country.
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