Pehlu Khan and others were injured after an attacked by a mob, who thought they were smuggling cows through Rajasthan.
The men had bought the dairy cows at a cattle fair and were taking them home to neighbouring Haryana state when the mob stopped the trucks.
Mr Prakash said the six others have now been discharged from hospital, adding that an examination would determine the cause of Khan's death.
Rajasthan's Home minister Gulab Chand Kataria said on Wednesday the vigilantes had "done a good job by protecting cows from smuggling". All of them were thrashed and their vans damaged.
Police said the mob stopped the trucks near Behror town, pulled out the men and beat them up. Of these, Pehlu Khan died at a hospital in Alwar on Monday night.
As per reports, Bahrod police station has registered a complaint against 200 people.
One officer, Ramesh Chand Sinsinwar, told the AFP news agency the men were transporting the animals without permission. For Pehlu Khan the attack proved fatal. PUCL general secretary Kavita Srivastava also demanded the arrest of SHO Behror and removal of SP Alwar over the incident. The assailants were believed to be members of right-wing groups Hindu Jagaran Manch and Bajrang Dal.
Critics say the vigilantes have been emboldened by the election in 2014 of Prime Minister Narendra Modi's Hindu nationalist Bharatiya Janata Party.
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'We do not support such incidents.
Yusuf shared with HT the two transport permits, one issued in the name of his brother, Azmat and the other, in the name of Irshad, another cow trader.
"We condemn such incidents".
The killing of a Muslim man by a group of alleged cow vigilantes has stirred a huge row with the state government choosing to book both parties in the case.
However, the police have even booked the transporters under the Rajasthan Bovine Animals (Prohibition of Slaughter & Regulation of Temporary Migration or Export) Act.
"Police had prior information that few people were smuggling cows. But they have violated the law by beating people brutally", he told ANI.
Police are regularly accused of working alongside cow-protection vigilantes and one state, Haryana, announced plans previous year to license some of the groups. Some of them fled.