Alleging that a mentally challenged man was hacked to death by his parents and younger brother, a mob assaulted them and ransacked their house in Garfa area of South Kolkata on Thursday, police said.
Policemen arrested the three after rescuing them from the attackers.
The mentally challenged man in his mid-20s, with cuts on his body, was taken to a local hospital by his parents on Wednesday night. He was declared brought dead.
After the incident came to light on Thursday, angry locals ransacked their house and thrashed the family members claiming that they murdered him.
"The mentally challenged man was declared dead after he was taken to a hospital. There are allegations he was hacked to death by his parents and his younger brother," a senior police official said.
Denying that they murdered the man, his family members said he was seriously injured after a fall in the bathroom on Wednesday evening.
"We arrested the man's parents and younger brother. Investigation is on. We have sent the body for post mortem examination," the police official said.