The vital clue? Food container used for abortive London bombs may hold key to attacks

Details of an unusual plastic container used to hold the home-made bombs in last Thursday's attacks on three Tube trains and a bus in London were released. Only 100 stores in Britain sell the Indian-made container, say police.

The hunt for the bombers became even more urgent with the disclosure that there is growing evidence of a fifth terrorist who dumped his bomb and fled.

One of the two men named as a potential suicide bomber was Muktar Said Ibrahim, 27, also known as Muktar Mohammed Said, who is accused of trying to blow up a No 26 bus in Hackney Road, east London, on Thursday.

Police raided a flat in north London yesterday where Ibrahim is thought to have lived. One neighbour said she had seen the suspect and another man bring large quantities of chemicals into the flat.

Police named the bomber who tried to detonate his device on the Tube at Warren Street on 21 July as 24-year-old Yasin Hassan Omar. The two men are thought to have been in Britain for several years, although they are believed to be of a Somalian background and their terror cell has links with east Africa. The Home Office refused to disclose whether they were living in Britain illegally.

The disclosure of a link to east Africa could have a big impact on the investigation into the attacks because it is likely to widen the focus of inquiries beyond Asian communities.

Deputy Assistant Commissioner Peter Clarke, the head of the Metropolitan Police's anti-terrorist branch, said the four suspects were all attempting to be suicide bombers. Video images from the Tube and the bus showed each man trying to detonate his rucksack or bag bomb. A small puff of smoke was seen, but none of the devices went off.

Police fear suicide bombers are more likely to strike again and, if cornered, would be prepared to kill rather than give themselves up.

Police have published the first details of components used to make the bombs. The explosives were placed inside plastic food storage containers that were then put in dark coloured rucksacks and sports bags.

The Delta 6250 containers are six-and-a-quarter litres in size and have white lids.

Scotland Yard appealed for any shopkeeper who had sold five or more of the containers to any customer to contact police.

Police have found a fifth bomb, which contained the same explosive as the other four devices, which were similar to the explosive used in the 7 July suicide attacks that claimed 56 lives. The device was found abandoned in bushes at Little Wormwood Scrubs in west London on Saturday.

The investigation by the police and MI5 is focusing on the addresses and associates of the four bombers captured on video.

Detectives were searching a flat at Ladderswood Way, New Southgate, north London, yesterday, where the suspect bus bomber, Ibrahim, is thought to have been.

Sam Jones, 33, a resident of the 12-storey housing block said she had seen Ibrahim carrying a large quantity of an unidentified chemical into the building with another man three or four weeks ago.

Ms Jones, who lives on the third floor, said: "They were carrying a huge number of small cardboard boxes into the lift. You could see boxes inside. There were about 50 in all.

"I asked them what was inside and they said it was chemicals for stripping wallpaper."

Residents said Ibrahim had been a regular visitor to the block in the past two years, staying for weeks at a time. They said he shared the flat with three Somalians, who played football in a nearby park once a week.

The one-bedroom flat at 58 Curtis House was occupied by a man in his 30s of Somali background who called himself George. He is also known as Ismail. He was said to have helped Ibrahim carry the cardboard boxes containing the chemicals.

Ms Jones said: "We all know him as George. He is a friendly, ordinary bloke. He always talks to the kids around here."

She added that she had last seen George on Friday but she not seen Ibrahim for about two weeks. Ms Jones said she had seen a third man of Somalian or Ethiopian appearance, who had been staying at the flat in recent weeks, clearing up a large amount of white powder that had been spilt in the hallway outside the flat.

Residents said the first they had known of the link between their flats, a high-rise block in a 1970s council estate, and the failed bus bomb was when they received a knock on the door at 1.15am yesterday. Tania Wright, 32, who lives on the eighth floor, below the raided flat, said: "I opened the door and there was a policeman in a peaked cap who said words to the effect there were terrorists in the building and we had to get out as soon as possible. As we went down the stairs you could see them all getting ready to go in. At the top was a Swat-style team with helmets and guns."

About 30 residents from the eighth, ninth and tenth floors of the flats were removed to a community centre before being allowed to return in the early hours. Forensic science teams erected a large tent in front of the building and could be seen removing plastic-wrapped items.

Two men, who do not include the four bombers, were arrested in the New Southgate area on Sunday and yesterday, on suspicion of terrorism offences.

Police are searching three other properties in London.

Officers revealed details yesterday of the movements of the four terrorists as they attempted to set off the suicide bombs.

Three of them went into Stockwell underground station just before 12.25pm on 21 July.

The first man tried to set off his bomb between Stockwell and Oval stations. After he failed, he was chased by members of the public but got off at Oval Underground and ran away.

The second man - Ibrahim - was seen getting on a No 26 bus in the Bank area of the City. He sat near the back of the bus and tried to set off his bomb. Having failed, he got off the bus.

The third man - Omar - tried to set off his bomb between Oxford Circus and Warren Street. Shortly afterwards, he escaped at Warren Street station.

The fourth bomber entered the underground at Westbourne Park station in west London at 12.20pm. At Shepherd's Bush, he tried unsuccessfully to set off his bomb. He then fled the train.

Investigators are exploring whether the group was working with at least one man of Pakistani background.