Police inspector Subodh Kumar Singh and a few other policemen were trying to control the mob when they were outnumbered and the situation went out of control.
"He worked with honesty and took all the responsibility upon himself. This is not the first incident when he faced the situation bravely. He had been hit by the bullet twice before. But now nobody is giving him justice. Justice will be done only when his killers are killed," Mr Singh's wife Sunita said.
Chief Minister Yogi Adityanath has declared Rs 40 lakh for Mr Singh's family, Rs 10 lakh for his parents and a government job for a family member.
The officer's sister said he had been killed because he had investigated the mob lynching of a Muslim man Mohammad Akhlaq in Dadri in 2015.
The autopsy report confirmed gunshot injury by .32 mm bore bullet on Mr Singh's head. So far, four people have been arrested in connection with the killing of the police officer.
"Law and order is usually good here but the police were kept in dark about the Islamic congregation that happened here, which caused chaos. This is the cause of this violence," said Bhola Singh, Bharatiya Janata Party minister from Bulandshahr.