Unanswered Questions from London Bombings

LONDON - Investigations into the deadly bombings on London on July 7 and the botched but similar attacks exactly two weeks later have left some key questions unanswered.

Four suspected suicide bombers killed themselves and 52 other people in attacks on three underground trains and a double-decker bus on July 7.

Two weeks later, police say four suspects failed in a bid to carry out a similar attack on London's transport system when their bombs did not detonate.

Here are some questions which remain unresolved, with background from police statements and media reports:

Were the July 7 Attackers Suicide Bombers?

British anti-terrorist chiefs say four young British Muslim men carried the bombs which exploded on July 7. London's police chief has also used the term "suicide bombers".

However some media have questioned whether the four men knew the bombs were going to explode when they did.

They have asked why the men did they not leave any pre-recorded messages, or shave their bodies like suicide bombers in the Middle East, and why the bombs were in rucksacks and not strapped to their bodies.

Commentators have also queried why the men left explosives, including a ready-made nail bomb, in a car at Luton station north of London before boarding a train to the capital.

However security experts say the men were clutching their devices as suicide bombers would and had made no attempt to hide their identities, indicating they had no intention of escaping.

They suggest the bombs could have been left in the car just in case the attacks failed or for other attackers to collect.

Why Did the Fourth Bomb Go Off Later?

Three of the July 7 bombs detonated on underground trains at 8:50 a.m. -- probably triggered by cell phone timers, according to a briefing by New York's police chief. Police have offered no explanation as to why the fourth bomber detonated his device on a bus almost an hour later.

One theory is the bus bomber had intended to set off his device on the underground railway's Northern Line but had to change his plans because it was suspended at the time.

Another suggestion is that the bomb was designed to cause maximum carnage by targeting commuters forced onto the bus after underground stations were closed due to the earlier blasts.

Were the July 7 and July 21 Attacks Linked?

The two attacks had many similarities, with bombers targeting three underground trains and a bus. New York police officials have also said the homemade explosives used in both attacks were similar.

Media reports say two of the July 7 bombers, Mohammed Sidique Khan and Shehzad Tanweer, went on a white-water rafting trip with friends a month before the attacks. Reports suggested there was a connection between individuals on the trip and the July 21 suspects.

But there is little evidence to directly link the attacks and police are treating them separately.

Were the July 21 Attacks Meant to Kill?

Hamdi Issac, one of the July 21 suspects who is being held in Rome, has told Italian magistrates his associates were an ad-hoc group who wanted to inspire fear because of the way Britons had treated Muslims following the first attacks.

He claims his bomb contained harmless materials and were never meant to explode.

British police have made clear they do not believe this assertion. Having examined the bombs, detectives say they could have caused many deaths. Police have not given a precise reason for the bombs' failure to explode but have made clear they believe Londoners were lucky to avoid more carnage.

Was There a Fifth July 21 Bomber?

A fifth partially-exploded bomb, similar those used in the July 21 attacks, was found abandoned in a north London park two days after the failed bombings.

That prompted speculation the device had been abandoned by a fifth bomber -- whose failed attack went unnoticed by members of the public -- or that one attacker had carried two devices.

A fifth man seized on the same day officers dramatically arrested two of the four prime suspects is reported by media to be a brother of named suspect Ramzi Mohammed.

Reports say detectives are investigating if he was the so-called "fifth bomber".

Was There a Mastermind/Master Bomber?

British police say the July 7 attacks bore the hallmark of al Qaeda. Security experts said the calculation and technical know-how suggested there was a mastermind behind the attacks.

However the four suspected suicide bombers are thought to have had no obvious links to terrorism and had never attended any al Qaeda training camps.

Al Qaeda's second in command Ayman al-Zawahri on Thursday warned of further attacks on London but did not claim responsibility for the previous bombings.

Police say they have to work on the assumption the group was not acting alone and they are hunting for accomplices.