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Two men entered Kanhaiya Lal's shop at a crowded market in Udaipur this afternoon and slit his throat with a cleaver. They tried to behead him but couldn't, said the police.
A video filmed by them showed Kanhaiya Lal measuring one of the men before he was attacked. The killers gloated on camera about the murder and also threatened Prime Minister Narendra Modi.
The police, who have declared curfew in parts of the city, said the killers fled and uploaded the video on social media. The leaves of all policemen have been cancelled and Udaipur is on alert.
The murder is being treated as a terror incident and a National Investigation Agency team is on its way to Udaipur, sources in the government have said.
Kanhaiya Lal had expressed support on social media for the former BJP spokesperson Nupur Sharma, whose provocative comments on Prophet Mohammed had set off a huge controversy at home and abroad. Sources said the tailor had been threatened several times by some groups even after his arrest over the social media post.
Senior police officer Hawa Singh Ghumaria, the Additional Director of law and order, told reporters they had received orders "not to spare anyone". Mr Ghumaria also asked the media not to broadcast the video because of its highly inflammatory content. "It's too grisly to watch. My advice is please don't look at the video," said the officer.
The police said the tailor had received threats from certain organisations after his posts in support of Nupur Sharma in the prophet remarks row. "On June 10, there was a police complaint against him... He was arrested and presented in court. On June 15, he told the cops he was being threatened. The police called all parties and community leaders to the station and the matter was resolved. The police is investigating the role of the community leaders who tried to broker peace in this matter," the police said.
Calling the situation "painful" and "shameful", Rajasthan Chief Minister Ashok Gehlot said an atmosphere of "animosity" has been created. "Strict action will be taken against all the criminals involved in this incident and the police will get to the bottom of it. I appeal to all parties to maintain peace," Mr Gehlot said.
"I appeal to everyone not to spoil the atmosphere by sharing the video of this incident. By sharing the video, the criminal's purpose of spreading hatred in the society will be successful," Mr Gehlot added.
"I have spoken to the Chief Minister, the Superintendent of police and asked that arrests be made as soon as possible so the anger simmers down," said opposition leader Gulab Chand Kataria of the BJP.