Police have stepped up their search for two mainland women suspected of drugging and robbing elderly men after luring them with offers of sex services, following the death of a man last week. The threesome sex ploy came to light in January, when police said the women were suspected of robbing at least a further four elderly clients between November and January. The most recent victim, 65, was found unconscious in his flat in Tak Tin Estate, Lam Tin, when his wife returned home last Tuesday. He died in hospital two days later. The flat had been ransacked, with gold ornaments and cash worth more than $10,000 missing, according to police. An autopsy initially failed to identify the cause of the victim's death and more examinations, including a toxicology test, were being carried out, a police spokesman said yesterday. A glass of water and other items found at the flat are understood to have been taken to the government laboratory for examination. Investigators are also checking footage from surveillance cameras at the housing estate to ascertain whether the victim had company at his flat. 'We do not rule out the possibility that the case is connected with the other four cases,' a police source said. The previous incidents occurred in Kwun Tong, Sau Mau Ping and Wong Tai Sin. In each case, several thousand dollars in cash and valuables was stolen after the victims were drugged. Police suspect the victims were fed a powdered sleeping potion in drinks or soup after inviting the two women into their homes. 'After consuming the drinks, some of the victims felt dizzy and some lost consciousness. It depended on how much of the drug they consumed,' the police source said. With their victims incapacitated, the women ransacked their homes and fled with cash and valuables, with each robbery taking less than an hour. Police believe the same two mainland women were involved in each of the five cases. Both of the suspects speak Cantonese and are thought to be aged between 20 and 30. They are described as about 1.55 metres tall, of thin build, while one has long hair. Police said the women targeted elderly men they found in public parks between 8am and 10am. The Kowloon East regional crime unit is investigating the five cases.