Ten people were killed and more than 20 were injured when an explosion tore through a train carriage in a St.Petersburg metro tunnel on Monday in what authorities called a probable terrorist attack Russian news media said police were searching for a man recorded on surveillance cameras who was thought to have been involved in the attack, which coincided with a visit to the city by President Vladimir Putin. Private television station Ren TV broadcast grainy pictures, it said were captured by a camera on board a metro train of a middle-aged man with a beard, a long black coat and black hat. Closed-circuit footage from a few minutes later showed him outside the station hit by the blast, looking at his telephone. Russia has been the target in the past of numerous bomb attacks, frequently targeting…