A teenager tried to blackmail a boy's father three days after the 11-year-old was strangled, saying the child would be killed or would have his hands and feet chopped off unless a ransom was paid, a court heard yesterday. Yu Ka-fai, 17, hatched a plot with Luk Yan-hong, 18, to kidnap an unnamed boy for a multi-million dollar ransom, the Court of First Instance heard yesterday. The pair allegedly recruited Luk's girlfriend, Chung Wai-yin, 26, and their friend Chan Sai-yip, 17, to help, the court was told. Prosecutor Robert Forrest said that on July 11 last year, Luk and Chung abducted 11-year-old Chan Chi-sin outside the American International School, Kowloon Tong, shortly after 12.30pm. They got in a taxi with the boy and went to Kai Yip Estate, Kowloon, where Luk lived, the jury of seven heard. Mr Forrest said two pictures obtained from a closed-circuit television camera on the estate showed the pair with the victim at 1pm. Some 40 minutes later, the camera showed Luk and Chung taking turns to carry the victim, who appeared either unconscious or dead, he said. Three days later, the boy's body was found in open space on Kai Yip Estate. A pathologist found the boy had been strangled three days earlier, the court heard. Police later found a roll of adhesive tape in Luk's flat that they believe was used to strangle the boy, the prosecutor said. Mr Forrest told the jury Yu had previously told his 13-year-old girlfriend about the plot and had said he would inject the boy with air to kill him before burying his body. It is the prosecution's case, however, that Yu had not participated in the kidnap or murder but had conspired with others to do so. Mr Forrest said Yu conspired with Luk to blackmail the boy's father, Chan Siu-kwan, and negotiated a sum of $1.4 million. On the phone to Mr Chan on July 14 last year, Yu was said to have threatened that his son would be killed or would have his hands and feet chopped off and sent home if he did not pay. On the same day, officers for the mainland's public security bureau arrested Luk and Chung in Fo Shan after Mr Chan had handed over the ransom money. Chung and Luk remain in custody on the mainland. Yu denied a charge of conspiracy to kidnap an unnamed person between an unknown date in June and on July 8 last year with Luk, Chung and Chan Sai-yip. He also pleaded not guilty to conspiracy to murder an unnamed person with Luk and Chung between the same dates and denied conspiracy to commit blackmail between July 13 and 14 last year. The trial continues today before Mr Justice Thomas Gall.