British police are engaged in one of their biggest manhunts on Saturday, scouring London's streets and houses for four suspects who botched their attempts to bomb the city's transport network. Police released images of the suspects hours after plain-clothes officers shot and killed a man in front of shocked passengers on an underground train following a chase. Armed officers later swooped on an apartment block in south London, arresting a man in connection with Thursday's failed attacks while rooftop snipers covered them. It was one of a series of raids across London by hundreds of police, some armed with assault rifles and machine guns. In the closed-circuit TV images of the suspects, the first man appears in a "New York" sweatshirt and a second man is shown in a white cap and a T-shirt with palm trees. Two others are in dark clothes, slightly obscured by a poor camera angle. The photographs splashed on the front pages of newspapers on Saturday put faces to the suspects as police appealed for help in finding them. It was unclear whether either the man police killed or the man they arrested was among the four suspects, who allegedly fled three subway stations and a double-decker bus on Thursday. Police also investigated an apparent attempt to set fire to the home of Jermaine Lindsay, one of the suspected bombers.