A four-year-old boy whose body was found stuffed in a nylon bag had vanished into thin air after meeting a stranger in the stairwell of a housing estate, the child's friend told police. Chan Fung-yu, now five, said he waited and searched in vain for his best friend, Yu Tze-fung, who disappeared after following a man who promised the children a 'precious' sword. In the Court of First Instance yesterday, jobless Yuen Wing-kong, 41, pleaded not guilty to murdering Tze-fung on October 10 last year. Prosecutor Mary Sin alleged Yuen strangled the boy after luring him to his flat in Un Chau Street Estate, Cheung Sha Wan, from the stairwell near Fung-yu's home on the same estate. Tze-fung's body was found in a nylon bag on the staircase between the second and third floor that night by a cleaner. Ms Sin alleged the defendant was seen dragging the nylon bag out of a lift that afternoon. Tze-fung was left with his friend that day while his father visited family members in Shenzhen. His mother did not have permanent residency at the time. In videotaped interviews shown in court yesterday, Fung-yu said he and Tze-fung were playing unsupervised in the stairwell with a toy sword when a stranger approached. 'He said, 'I will give you a precious sword, a sword which is luminous and can make sounds',' Fung-yu said. 'The [man] told us to go to the fourth floor . . . I said I didn't want it. Then I told Yu Tze-fung not to go. Then unexpectedly, he went there. 'Then I was told to wait for him there. But I didn't see him again. Then I went to the fourth floor to look for him, but failed to find him.' The four-year-old returned home but was sent back out alone by his 12-year-old sister to look for his missing friend. The child returned twice to the place where Tze-fung disappeared, once on his own and again with a different friend. Eventually Fung-yu's sister alerted the rest of the family and when their search proved fruitless, Tze-fung's father, Yu Man-kwong, was contacted. The 34-year-old father broke down in court as he recalled the last time he saw his son alive on the same day. The trial continues before Mr Justice Frank Stock.