The city police authorities have ordered a change of investigating officer (IO) in a case that started less than a fortnight ago.

IO M.K. Deb of Posta police station, probing the beating up of a septuagenarian advocate outside his Kalakar Street residence, in central Calcutta, allegedly by one of his tenants and his son, was replaced by B.K. Biswas on Monday.

?The officer was changed for the sake of proper investigation,? said deputy commissioner of police (central) Ajay Kumar on Tuesday.

The alleged victims expressed surprise at the sudden change in IO.

The incident took place on April 22, when C.L. Saraf, the advocate, and his son Anand were returning home after a meeting at Posta police station.

The two were asked to visit the police station following a court order over a dispute with the tenants of their house.

Saraf had let out portions of the building to businesses. At the police station, he met his tenant Ramgopal Kanoi and his son Arun.

After the meeting, the advocate and his son set out for home on foot, while Kanoi and his son rode home on a scooter.

?On reaching our house, we found a scooter obstructing the entrance. Suddenly, Kanoi and his son, who were hiding, attacked us,? said Saraf.

The Kanois hit him repeatedly with a helmet, causing serious injury to his right arm, the advocate alleged.

?They also kicked me and even tried to kill me,? Saraf wrote in his complaint.

Anand said that he, too, was seriously injured by the attackers when he tried to rescue his father.

Local residents accompanied the Sarafs to the police station after the incident. After lodging their complaint, the father and son visited a central Calcutta hospital for treatment. Saraf?s right arm was found to have been fractured. He was later admitted to a nursing home.

Kanoi and his son were not available for comment.

Deputy commissioner Kumar said that one person was arrested in connection with the incident. ?We are trying to find out what had actually happened,? he said.

Anand said on Tuesday that the change of IO soon after the probe started showed that the police were not attaching much importance to the incident.

?Although the father and son secured anticipatory bail from the court yesterday, we are hopeful that justice will prevail,? he added.