A TEENAGER who robbed a police constable's mother-in-law was caught when he walked past the victim at a food stall two weeks later, the District Court heard yesterday. The victim, Ms Li Pui-ling, was followed by two men as she got into a lift at Shek Wai Kok Estate, Tsuen Wan, on October 15 last year, the court was told. One was the defendant, Ma Wai-ming, 16, who yesterday pleaded guilty to robbing four women of gold necklaces. Ms Li tried to leave the lift at the 26th floor, but one of the pair grabbed her by the neck from behind and the other hit her twice on the back and snatched a gold necklace and pendant. The pair then fled downstairs. About two weeks later, Ms Li was having a meal with her family at a food stall at the Shek Wai Kok Estate commercial complex when Ma walked past. She was with her son-in-law, a police constable, and told him about the defendant. Ma was stopped and subsequently arrested. Under caution, he admitted having robbed the victim and selling her gold necklace and pendant to a goldsmith's shop for $1,600. The court heard that Ma had robbed three other women in lifts on Shek Wai Kok Estate last October. In mitigation, defence lawyer Mr Joseph Poon said that the root of Ma's problem was his drug addiction. Judge Lugar-Mawson sentenced Ma to a drug addiction treatment centre.