A MAN masquerading as a police officer sexually assaulted and robbed a 15-year-old schoolgirl, the District Court heard. The girl told the court that on the evening of March 7 she and her boyfriend were at the playground in Yuen Long Park when a cyclist stopped to ask questions. Chan Kat-chun, 31, has pleaded not guilty to robbery, impersonating a police officer, and sexual assault. The court heard Chan told the couple he was a police officer, and asked the girl to go with him to a more secluded part of the park. He had asked if she was a virgin and if she had ever been sexually assaulted. He shoved his hand under her shirt and fondled her, the court heard. 'He told me to stretch my legs apart and not to be stubborn,' the girl said. 'I dared not shout because he told me he had a gun.' The girl said Chan told her to hand over a gold bracelet and that she would only get it back by going to bed with him. He then grabbed her gold necklace and fled on his bike, she said. On March 17, the girl and her mother went to Tai Po police station where she identified Chan from a photograph. The trial continues before Judge Bokhary.