LONDON - Police investigating this week's attempted subway and bus bombings said Saturday they arrested a second man in the same south London neighborhood where officers already had detained one suspect and shot another dead in front of horrified commuters.

Two days after the second terrorist attack in London in as many weeks, thousands of officers fanned out in a huge manhunt amid hopes the publication of images of four suspected attackers would lead to their capture.

The Metropolitan Police said the second arrest late Friday was "in connection with our inquiries" into Thursday's attacks.

The bombs failed to detonate properly and no one was injured in the attacks.

Police said they had a good response to the release of the photos, taken from the British capital's ubiquitous closed-circuit surveillance cameras.

The startlingly clear closed-circuit TV images of the suspects stared from the front pages of British newspapers Saturday. "Faces of the four bombers," said the Daily Telegraph. "The Fugitives" said The Times, while the Daily Mail labeled them "Human Bombs."

One image shows a stocky man in a "NEW YORK" sweat shirt running through a station. Another depicts a man in a white baseball cap and a T-shirt adorned with palm trees. Two others are in dark clothes, slightly obscured by a poor camera angle.

Heavily armed officers patrolled the British capital with clear instructions to stop suicide bombers - if necessary, with a shot to the head.

"If you are dealing with someone who might be a suicide bomber, if they remain conscious, they could trigger plastic explosives or whatever device is on them," said Mayor Ken Livingstone.

Some Muslims and civil libertarians expressed concern about the police's Stockwell station shooting of the suspect - described by witnesses as being of South Asian appearance and wearing a heavy padded coat. Police chased him into a subway car, pinned him to the ground and shot him in the head and torso, an eyewitness said.

"They pushed him onto the floor and unloaded five shots into him," passenger Mark Whitby told the BBC. "He looked like a cornered fox. He looked petrified."

Metropolitan Police Commissioner Ian Blair said the shooting was "directly linked" to the investigation.

"The man who was shot was under police observation because he had emerged from a house that was itself under observation because it was linked to the investigation of yesterday's incidents," police said in a statement. "He was then followed by surveillance officers to the station. His clothing and his behavior at the station added to their suspicions."

Police haven't said whether the suspect was carrying a bomb.