Police in northern India have arrested four people for their alleged involvement in an attack on police over rumours of cow slaughter that left two people dead, including a police official.

Senior police officer Pravin Kumar said on Tuesday that a case was filed against 28 people who allegedly set a police outpost on fire and killed a local police inspector. Another man also died in the violence.

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The incident took place on Monday in the city of Bulandshahr in Uttar Pradesh state. The area is 300 kilometers (200 miles) southwest of Lucknow, the state capital.

The chaos began after beef and a few animal bones were found in a field in a village.

Cow slaughter is banned in parts of India, including Uttar Pradesh.

Kumar said police arrested four people and were looking for the main suspect, Yogesh Raj. While it was not clear if any hard-line groups were behind the attack, Raj is alleged to be a member of right-wing Bajrang Dal, the youth wing of Vishwa Hindu Parishad, a Hindu group that opposes cow slaughter.

On Monday, the villagers blocked a road, demanding the responsible be arrested for slaughtering cows, Kumar said. When police asked them to lift the blockade, they attacked police, he said.

“Soon, the protesters outnumbered police,” he said. “They snatched arms, mobiles and cartridges of police. The policemen retreated. Someone from the crowd opened fire that killed the police inspector.”

The crowd also torched a police outpost, police jeeps and a few private vehicles during the violence, he said.

Opposition parties blamed the Hindu nationalist government of Prime Minister Narendra Modi for patronizing hard-liners in the name of protecting cows.