LONDON (Reuters) - British police are chasing down the people they suspect of being behind a bomb which injured 29 people on a packed commuter train in west London on Friday, the country s most senior counter-terrorism officer said.  Mark Rowley said officers were sifting through surveillance footage and examining the remains of the device.  This is a very complex investigation which is continuing at speed,  he told reporters.  We are chasing down suspects.  
British police 'chasing down suspects' after train bombing