A three-year-old girl watched her grandfather stab her mother to death, then inflict a fatal wound to himself in their Tin Shui Wai home yesterday. Lam Yee-kwan saw her mother, Kuen Koon-lei, 38, bleed to death in the sitting room. She stayed with the body for more than four hours until her 11-year-old sister came home from school. She was too scared to scream or call for help and was unable to flee the flat because her mother's body blocked the front door. Her ordeal ended when her older sister returned to the 10th-floor flat at Yiu Man House shortly before 1 pm and a neighbour helped push the front door open. The sisters were in shock and being cared for by the Child Abuse Investigation Unit and social workers at Tuen Mun Hospital. Lam Yat, the 65-year-old father-in-law, was found on the bed in his room with knife wounds to his neck and chest. He died in Tuen Mun Hospital last night. The killing took place at about 8 am when the mother, who worked in the accounts section of a Mongkok firm, was due to take the three-year-old to kindergarten. The older daughter had already left and their father had gone to work at the Chek Lap Kok site. A police investigator said initial investigations showed the grandfather had attacked the woman in the heat of an argument and then stabbed himself. 'We believe the tragedy was sparked by a long-standing disagreement on family affairs between the woman and her father-in-law,' he said. The couple is understood to have another child on the mainland being looked after by relatives. They have lived in the flat since 1992.