Police launched a murder investigation yesterday after arresting seven more youths in connection with the death of an 18-year-old woman in Yau Tong. Ten young people - six males and four females aged 13 to 20 - have now been arrested. The first arrests were made on Friday when three youths believed to be friends of Lau Mei-ying, were detained. Police last night took some of the suspects to Sau Mau Ping for evidence gathering. The case came to light on Thursday morning when a cleaner found Lau lying unconscious on a staircase in Kai Tin Road. She was declared dead at the scene by ambulancemen. Lau, who weighed 104kg, left her home in Cha Kwo Ling two weeks ago saying she was possessed by spirits and wanted to lose weight. Police suspect she died elsewhere and that her body had been moved to the scene. A postmortem examination could not determine the cause of death. There were no broken bones, she had suffered no visible wounds and there were no injuries to any of her internal organs. Police are also investigating three other deaths that occurred on Thursday. In Sheung Shui, a 53-year-old man was stabbed in Wah Shan Tsuen near Tin Ping Road and died in hospital. His son, 21, was charged with murder on Friday and appeared in Fanling Court yesterday morning with another man, also 21. No pleas were taken and the case was adjourned until August 23. And officers in Causeway Bay are investigating a possible murder-suicide after a prostitute had her throat slashed and a man, believed to have been a client, jumped from the roof of her building in Lee Garden Road.