LONDON -- Investigators hunting four fugitives wanted for the abortive bombing of the city's transit system last week have linked them to the four presumed suicide bombers who killed 52 bystanders and wounded 700 others two weeks earlier, a British official said yesterday.
Meanwhile, the country's highest-ranking police officer apologized for the killing of a Brazilian man at a subway station Friday by plainclothes officers who mistook him for a suspected terrorist.
The slain man's relatives and friends rejected the explanation for the shooting of Jean Charles de Menezes, a 27-year-old electrician who was on his way to a job when he was chased into a subway car by undercover policemen who shot him in the head five times in front of horrified passengers.
An official confirmed reports that investigators found a brochure for a white-water rafting company in Wales in a backpack crammed with explosives that one of the fugitives left on the upper deck of a double-decker bus in east London on Thursday. Earlier, police had determined that at least two of the suicide bombers from the deadly July 7 attacks -- Mohammad Sidique Khan, 30, and Shehzad Tanweer, 22 -- had taken part in a rafting trip at the company's center in June.
Police are investigating the possibility that all eight men met that day, said the official, who spoke on condition of anonymity, and might have been brought together by another person who helped coordinate the attacks and may provide a link to the Al Qaeda network.
One working police theory is that Thursday's would-be bombers, whose backpacks of powerful homemade explosives failed to detonate, are from a cell of northern Africans living in the London area, the official said. The men who police allege carried out the July 7 attacks were British Muslims, three of them of Pakistani origin from the northern England city of Leeds, the fourth a Jamaican-born convert to Islam.
The other potential link is the explosives. Investigators believe triacetone triperoxide was used in both sets of attacks, though they have not conclusively identified the substance in the July 7 attacks. Traces of it were found in the pipes of a tub in a Leeds apartment believed to have been rented by one of the bombers, as well as in nine small bombs found in a rental car left by one of the men in a train station north of London.
Police announced they arrested an unidentified man yesterday evening. He is the third man being held for questioning under anti-terrorism laws since the failed bombings on three subway trains and a bus that injured one person but mirrored the deadly strike two weeks earlier.
While detectives hunted the would-be bombers, Police Commissioner Sir Ian Blair offered his ''deep regrets" to the Menezes family for Friday's shooting but said police would not change the shoot-to-kill policy when facing what it deems a terrorist threat.
Blair said that when confronting suspected suicide bombers who might have explosives strapped to their chest, ''the only way to deal with this is to shoot in the head." He pledged the killing would be investigated.
According to the official account, plainclothes officers who received information tracing a suspected terrorist to an apartment bloc in south London mistakenly followed Menezes when he emerged from one of the buildings. Police said he was wearing a baseball cap and heavy jacket on a warm day, and they suspected he might be carrying explosives. When he got off a bus and entered the Stockwell subway station, they raced after him and shot him to death in a subway car.
''Apologies are not enough," said cousin Alex Alves Pereira. ''I believe my cousin's death was result of police incompetence."