Updated at 11.38am: A 23-year-old man was arrested in Ma On Shan early on Tuesday morning after three motorcycles were set alight. ''A number of arson cases have occurred in Ma On Shan these past few months. We have reason to believe he may be related to them,'' a police spokesman said. Police officers attached to the Task Force Sub-unit of Ma On Shan Division laid an ambush near Wu Kai Sha Village shortly after midnight. At about 2.20am, a man approached three motorcycles parked in an open space in the village and set fire to the vehicles. Police officers pounced on the man, surnamed Wong, and found two lighters in his possession. He was arrested for arson and is presently being detained.