LONDON - Police believe they have identified all four suicide bombers who carried out the deadly attacks on London subway trains and a bus last week, the city's police chief said Thursday.
Metropolitan Police Commissioner Ian Blair told the Foreign Press Association that police believe "that we know who the four people carrying the bombs were ... and we believe they are all dead."
"We are as certain as we can be that four people were killed and they were the four people carrying bombs," Blair said.
His comments were the first public confirmation from police that the July 7 attackers were suicide bombers. Bombs exploded on three subway trains and a double-decker bus, killing at least 53 people, including the attackers.
Peter Clarke, head of the Metropolitan Police anti-terrorist branch, on Thursday identified the suspected suicide bomber who blew up the double-decker bus, killing 13 people, as Hasib Hussain, 18. Clarke also said Shahzad Tanweer, 22, was responsible for attacking a subway train between the Liverpool Street and Aldgate stations. Both are Britons of Pakistani descent.
News reports have identified the other two as Mohammed Sidique Khan, 30, another Briton of Pakistani descent, and Lindsey Germaine, a Jamaican-born Briton.
Blair declined to comment on those reports, and he would not say how many suspects are being sought.
"We don't know if there is a fifth man, or a sixth man, a seventh man," he said, but added that police were trying to determine who organized the attack.
Two claims of responsibility purportedly from militant Islamic groups have surfaced.
Commenting on the possible role of al-Qaida, Blair said, "Al-Qaida is not an organization. Al-Qaida is a way of working ... but this has the hallmark of that approach."
"Al-Qaida clearly has the ability to provide training ... to provide expertise ... and I think that is what has occurred here," Blair said.
The Times of London, quoting unidentified police sources, said detectives were interested in locating Magdy el-Nashar, 33, an Egyptian-born academic who recently taught chemistry at Leeds University. The Times said he was believed to have rented one of the homes being searched in Leeds.
A spokesman at North Carolina State University said el-Nashar studied chemical engineering there, beginning in January 2000.
Saad Khan, the chemical engineering department's director of graduate programs, said he remembered that el-Nashar applied for admission while living in Egypt. By the end of spring semester in 2000, el-Nashar had decided to pursue a doctorate at Leeds instead, Khan said.
In a statement Thursday, Leeds University said el-Nashar enrolled in October 2000 to do biochemical research, sponsored by the National Research Center in Cairo, Egypt. It said he earned a doctorate May 6.
"We understand he was seeking a postdoctorate position in the U.K.," the university said. "His visa was updated by the Home Office earlier this year. He has not been seen on the campus since the beginning of July."
Neighbors said el-Nashar recently left Britain, saying he had a visa problem, The Times reported.
The Daily Telegraph said police were trying to identify a man seen standing near the four suspects on the Luton railway station platform, where they apparently boarded a train for London on July 7.
The Evening Standard reported that police spotted a fifth man on closed-circuit TV of the group at London's King's Cross station about 20 minutes before the explosions.
Late Wednesday, Scotland Yard said anti-terror police had raided a residence northwest of London.
Officers carried out a forensic examination, but police would not say why they targeted the house on a residential street in Aylesbury, about 40 miles from London and 20 miles from Luton - where a vehicle believed to be linked to the attacks was towed away Wednesday.
Reports said Tanweer had been arrested once for shoplifting, and Hussain was once questioned for disorderly behavior.
The Independent newspaper, citing police sources, said one of the four had been linked loosely to a plot to build a large bomb near London. It did not identify the suspect. The newspaper said police described the link as a low-level "association."
That appeared to be a reference to a ring cracked in March 2004, when eight men were arrested across southern England in an operation that led to the seizure of half a ton of ammonium nitrate, a chemical fertilizer used in many bomb attacks. Several have been charged and face trial.