Police on Monday released the names of two of the four men suspected of taking part in the failed July 21 bombings and said a fifth device similar to others used in the botched attacks was found in a west London park.

Prime Minister Tony Blair (search) apologized Monday for the police killing of a Brazilian electrician mistaken for a terrorist. Britain's police complaints commission later said the man, Jean Charles de Menezes, 27, was shot eight times.

Peter Clarke, head of the Metropolitan Police anti-terrorist branch, released new images of some of the men who tried to bomb three subway cars and a bus. He identified two of the suspects as Muktar Said Ibraihim, also known as Muktar Mohammed Said (search), 27, and Yasin Hassan Omar (search), 24.

Police also said they arrested two more suspects Monday in connection with last week's attempted attacks, bringing to five the number in custody.

Police did not release any details of the arrests, except to say they were not carried out at the home of one of the four suspected bombers being searched. A police spokeswoman, who asked not to be identified in accordance with British practice, would not say where the two were arrested.

Two other men were arrested in London's southern Stockwell neighborhood Friday and one was arrested Saturday in nearby Tulse Hill — all "on suspicion of the commission, instigation or preparation of acts of terrorism" for the July 21 attacks, when bombs only partially detonated and no one was injured.

Clarke said one of the suspects, who was not identified but was shown in a closed-circuit TV image wearing a "New York" sweatshirt, was chased in the Oval station by "extraordinarily brave members of the public who tried to detain him." Giving them the slip, the man ran out into the Brixton neighborhood, where police found his sweatshirt.

Police believe the other unidentified man, who tried to set off a bomb near the Shepherd's Bush station, probably climbed through a window at the end of the carriage when the device failed to go off.

"He then made his way along the track for about 200-300 yards, before climbing down into back gardens and making good his escape," Clarke said.

Omar was last seen vaulting over a ticket barrier at Warren Street station and running toward the exit.

Said, wearing a white baseball cap and a shirt with a palm-tree design, was caught on camera stepping off the bus in the Hackney district.

In making his apology, Blair also defended the police for Friday's shooting.

"We are all desperately sorry for the death of an innocent person and I understand entirely the feelings of the young man's family, but we also have to understand the police are doing their job in very, very difficult circumstances," Blair said.

"Had the circumstances been different and had this turned out to be a terrorist, and they had failed to take that action, they would have been criticized the other way."

The British Broadcasting Corp. reported that Menezes' visa had expired, suggesting this may have been why he ran from police Friday before being shot. However, Menezes' cousin said the visa was still valid.

Menezes' family on Monday threatened to take legal action.

"They have to pay for that in many ways, because if they do not, they are going to kill many people," his cousin, Alex Pereira, told BBC television. "They killed my cousin; they could kill anyone."

Menezes was followed by plainclothes officers after he left an apartment bloc in Tulse Hill that was under surveillance. Wearing a padded jacket, he boarded a bus and traveled to the nearby Stockwell subway station. According to officials, his clothing and behavior aroused the suspicions of police, who ordered him to stop.

Witnesses said Menezes ran into a subway car, where officers shot him. It was unclear why Menezes, who spoke English, did not stop.

Investigators are pursuing leads that seemed to indicate a link between the July 21 attacks and the homicide bombings two weeks earlier that killed the four bombers and 52 other people.

Police say they are looking for more suspects because investigators believe a wide network of Al Qaeda-linked operatives staged the attacks. The network could include bomb-makers and those who coached the young attackers before their mission, according to police.

Metropolitan Police Commissioner Sir Ian Blair said he believed Al Qaeda terrorists were involved in both attacks.

"The way in which Al Qaeda operates is not a sort of classic cell structure," Ian Blair told Britain's Sky News television on Sunday. "It has facilitators, so we're looking for the bomb makers, we're looking for the chemists, we're looking for the financiers, we're looking for the people who groomed these young people, so it will be a wide network that we're trying to penetrate."

Asked if the two attacks were connected, Ian Blair said "we have no proof that they are linked, but clearly there is a pattern here."

In releasing the two suspected bombers' names, Clarke said an "initial forensic examination of the four partially detonated bombs has revealed clear similarities" with a fifth device found in west London's Little Wormwood Scrubs park. The bomb, in a dark-colored backpack, was found Saturday and blown up Sunday.

All five of the bombs were in the same type of plastic food storage container and put into dark-colored backpacks, Clarke said. He said the food containers, manufactured in India, were sold in about 100 stores around Britain, and he appealed to shopkeepers to call police if they remembered anyone buying them.

Police were reportedly investigating whether some of the July 21 suspects may have visited the same Welsh whitewater rafting center as two of the July 7 homicide bombers: Mohammed Sidique Khan and Shahzad Tanweer.

The two bombers went whitewater rafting there June 4, according to the National Whitewater Center. Police have refused to comment on reports that a brochure for the rafting center was found in an explosives-laden knapsack that failed to detonate on a bus July 21.