LONDON – British police yesterday identified two of four men believed responsible for last week’s botched transit bombings and said an explosive found in a park was like those used in the attempted attacks, raising fears a fifth bomber was on the loose.

London’s police chief said the force was “racing against time” to find the bombers, who fled three subway trains and a bus when their devices failed to fully detonate. Those bombs and the one found abandoned Saturday all were made using clear plastic food storage containers put into dark-colored bags or backpacks.

At a televised press conference, the head of the Metropolitan Police antiterrorist squad, Peter Clarke, held up one of the white-lidded, 1.65-gallon containers – called a Delta 6250 – and urged any shopkeeper who had sold five or more of them to contact police.

Earlier, Prime Minister Blair apologized for the killing of a Brazilian electrician mistaken for a terrorist as officials confirmed that undercover police shot him eight times – one in the shoulder, seven in the head. Mr. Blair also urged Britons to come forth with information on the fugitive bombers.

Police identified two of the suspects as Yasin Hassan Omar, 24, and Muktar Said Ibrahim, 27, also known as Muktar Mohammed Said, but did not give their nationalities.

Authorities also released new closed-circuit images of the four suspects and gave details of their movements, recounting how one bolted from a subway station pursued by passengers, while another jumped through a subway window and fled down the tracks.

Armed officers raided a London apartment that Mr. Said – suspected of trying to bomb a bus in east London on Thursday – was believed to have visited recently. Forensic officers in white overalls searched the apartment in Curtis House, a concrete high-rise in the city’s northern suburbs.

Resident Sammy Jones, 33, said she thought she recognized a man who visited the building as Mr. Said. She said he stayed with an African named George who lived in a ninth-floor apartment. Ms. Jones said two men of Somali appearance also visited the apartment.

“They used to come in at all hours of the night,” she said. She said a few weeks earlier she had seen George and the man she thought was Mr. Said filling an elevator with small brown cardboard boxes. When she asked what was in them, they replied “wallpaper stripper.”

Metropolitan Police also said yesterday they had arrested two people on suspicion of terrorism in the area but not at the raided address. Three other suspects are already being questioned at a high security London police station “on suspicion of the commission, instigation, or preparation of acts of terrorism” in connection with the July 21 attacks.

On Sunday, police destroyed a package found by a passer-by in bushes in a west London park not far from the scene of the attempted bombing at Shepherd’s Bush station. Mr. Clarke said forensic examination showed “clear similarities” between the device and the four bombs found Thursday.

Those attacks came two weeks after bombings that killed 52 people and four suspected suicide bombers on three subway trains and a double-decker bus.

Police Commissioner Ian Blair said police were mounting “an absolutely brilliant operation, and it is, of course, racing against time.” But as the investigation rolled on, police faced growing criticism over the killing of the unarmed Brazilian mistaken for a potential bomber.

The family of Jean Charles de Menezes, 27, shot dead Friday inside a subway carriage in front of horrified passengers, said they were considering legal action against the police.

As a coroner’s inquest opened yesterday into the shooting, Mr. Blair expressed “sorrow and deep sympathy” over the death but said police were working “in very,very difficult circumstances.”

“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 prime minister said.

The police commissioner has indicated he believed Al Qaeda-linked terrorists were involved in both the July 7 and July 21 attacks. Asked if the attacks were connected, he said: “We have no proof that they are linked, but clearly there is a pattern here.”

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 suicide bombers, Mohammed Sidique Khan and Shahzad Tanweer.

The men went rafting there June 4, according to the National Whitewater Center. Police have refused to comment on press reports that a rafting center brochure was found in the explosives laden knapsack found on a bus July 21.