London ? The emergence of suspected links between last week’s attempted transit bombings and the deadly July 7 blasts here make it increasingly likely that a single terrorist network directing multi-ethnic, British-based cells was behind both plots, officials said Sunday.

As the investigation continued, police on Sunday announced the arrest of a man in a working-class area of South London, where authorities have conducted a manhunt for the four fugitives whose backpack bombs failed to detonate on three trains and a bus Thursday. Few details were given about the suspect, who was held under anti-terror legislation along with two other men arrested in South London on Friday. Police have not said if any of the three are among the four fugitive bombers.

South London is an area with large populations of Africans and Afro-Caribbeans, and is one of several longtime bastions of Islamic extremism in Britain. One of detainees is said to be of Ethiopian descent. One of the fugitives – who was identified partly through evidence found in an unexploded backpack bomb – apparently has family ties to another African country, according to a senior European police official working with British investigators.

In the July 7 bombings that killed 56 people, three of the attackers were Pakistani-Britons from the northern city of Leeds, and one was a Jamaican convert to Islam living in Luton north of London.

The targets, methodology and bombs used in both cases were very similar, investigators say. Now, detectives are investigating evidence found in the unexploded backpack bombs that might place members of both cells at the same rafting center in Wales last month, according to officials and news reports.

Police officers guard the road leading to Scotia Road Sunday in Tulse Hill, south London, where a person linked to the July 21 attempted bombings was arrested.

“The evidence in the backpacks has given good leads,” the European police official said. “Everything seems to connect the two cases.”

Rafting ‘extravaganza’

Four weeks before they died, two of the July 7 suicide bombers went on a rafting trip in the pristine wilderness of the Tryweryn River.

Mohamed Sidique Khan, 30, and Shezhad Tansweer, 22, participated in a six-person group that took a two-hour “extravaganza” rafting tour June 4, said Paul O’Sullivan, the director of the National Whitewater Center in north Wales.

A photo of the two future bombers wearing helmets and bulky wet suits and wielding oars, their raft churning up surf, appeared in a British tabloid last week. In the shot, Khan – the suspected leader of the bombers – smiles and flashes a “victory sign” with his right hand.

Police have questioned employees of the center, known in Welsh as Canolfan Tryweryn, about Khan and Tansweer. The center has provided police with a list of other participants, O’Sullivan said.

Suspects identified

Using documents found in the backpack bombs last Thursday, detectives have identified suspects and are investigating whether one or more of them crossed paths with Khan and Tansweer at the rafting center, officials said.

With a mix of awe, fear and indignation, neighbors on Sunday described how the raid began: a fleet of about eight BMW sedans carrying an elite anti-terror squad led a caravan of well-armed police raiders roaring down the curved driveway past a playground to the main entrance.

The police shouted at neighbors to take cover as they charged into Scotia Street, a short cul-de-sac, witnesses said. Neighbors said they heard as many as 12 detonations that they believed were gunshots.

“They were yelling ‘Get inside, get inside’,” said Joshua Romans, a soft-spoken 17-year-old with braided hair who lives a few doors away from the residence that was raided. “About five or ten minutes after, there were five shots. After that there was another three, then four. About 12 shots altogether.”

But police said nothing publicly about any gunfire. In previous raids they have detonated tear gas canisters as they enter buildings.

And neighbors said they knew nothing about the suspect who was taken away as white-suited forensics teams hunted for the slightest trace of the elusive bombers.