The Park Side Road house where Shyama Prasad Roy lived. A Telegraph picture

Shyama Prasad Roy was asphyxiated, the post-mortem has revealed. The 54-year-old advocate’s decomposed body was found in his apartment, off Rasbehari Avenue, on Thursday.

Doctors found an injury on the back of Roy’s head, possibly caused by a blunt weapon. A scuffle with the murderer may have resulted in the blow, said police.

Roy was found kneeling on his bed with both hands tied behind, feet trussed and a gag stuffed into his mouth. His neighbour Laltu Mukherjee sounded an alarm after a foul smell started coming out of the flat. The advocate was last seen on Tuesday.

“The killer probably tried to make Roy unconscious and then gagged him after tying his hands and legs,” said an investigator.

The police are clueless about who the killer could be. “It appears that there was more than one assassin and they were probably known to the deceased. We are preparing a list of people who were in regular contact with Roy, including real estate brokers, materials suppliers and his friends,” said Jawed Shamim, the deputy commissioner of police (south division).

“Roy owned the three-storey building on Park Side Road. He recently started selling out flats on the first and second floors. We are trying to find out whether he had any rivalry with local realtors,” said another officer.

The police found one of the two cellphones belonging to Roy missing.

“We have contacted the service provider that issued the SIM card and asked for the call details,” said an officer of Tollygunge police station.

The police tried to contact the people whose numbers were found in Roy’s cellphone, but all the phones were switched off.

The investigators believe that the killer was close to Roy and killed him to acquire his property.