A 78-year-old man was arrestedon Sunday for allegedly killing his differently-abled son who denied to wear a mask while stepping outside home, police said.Banshidhar Mallick, a resident of Shovabazar Lane here surrendered at the Shyampukur Police Station on Saturday evening, claiming to have killed his son Shirsendu (45), they said."The elderly man came to the police station and said he killed his physically-disabled son at their residence by strangulation with a cloth around 5.30 pm," a senior police officer said.Officers of the police station found Shirshendu's body on the floor in one of the rooms of the house.The body has been sent for post-mortem examination, he said, adding, a case of murder was initiated against the senior citizen.Further investigation is underway, police said.