Goa Police are yet to trace the origins of the letter which threatened to harm PM Narendra Modi and Defence Minister Manohar Parrikar. “We are still inquiring into the origins of the letter. The inquiry is going on," Inspector General of Police (IGP) V Renganathan said on Wednesday. He said security has been beefed up across the state and all precautions are being taken. On asked whether the letter purportedly signed by ISIS, could be a prank, he said probe is underway into all aspects but the threat has been taken seriously.