Why did they buy return train tickets to Luton? Why did they buy pay & display tickets for cars? Why were there no usual shouts of 'Allah Akhbar'? Why were bombs in bags and not on their bodies?
The London bombers may have been duped into killing themselves so their secrets stayed hidden.
Police and MI5 are probing if the four men were told by their al-Qaeda controller they had time to escape after setting off timers. Instead, the devices exploded immediately.
A security source said: "If the bombers lived and were caught they'd probably have cracked. Would their masters have allowed that to happen? We think not."
The evidence is compelling: The terrorists bought return rail tickets, and pay and display car park tickets, before boarding _ a train at Luton for London. None of the men was heard to cry "Allah Akhbar!" - "God is great" - usually screamed by suicide bombers as they detonate their bomb.
Their devices were in large rucksacks which could be easily dumped instead of being strapped to their bodies. They carried wallets containing their driving licences, bank cards and other personal items. Suicide bombers normally strip themselves of identifying material.
Similar terror attacks against public transport in Madrid last year were carried out by recruits who had time to escape and planned to strike again.
Bomber Hasib Hussain detonated his device at the rear of the top deck of a No 30 bus, not in the middle of the bottom deck where most damage would be caused.
Additionally, two of the bombers had strong personal reasons for staying alive.
Jermaine Lindsay's partner Samantha Lewthwaite, 22, mother of his one-year-old son, is expecting her second baby within days. Mohammed Sidique Khan's wife Hasina, mum of a 14-month-old daughter, is also pregnant.
Our source disclosed: "The theory that they were not a suicide squad is gathering pace. They were the weakest link.
"We think it's possible they were told that when they pressed buttons to set off timers they'd have a short time to abandon the bombs and get away before the blast. Instead, the bombs exploded immediately."
Another intelligence source added: "Whoever is behind this didn't want to waste their best operatives on a suicide mission. Instead they used easily recruited low-grade men who may have believed they'd walk away."
At least 54 people were killed in the 7/7 blasts. Khan, 30, of Dewsbury, Shehzad Tanweer, 22, of Leeds, and Jamaican-born Lindsay, 19, of Aylesbury, Bucks, detonated devices on the Tube at Edgware Road, Aldgate and King's Cross.
Hussain, 18, of Leeds, blasted the bus at Tavistock Square. The Tube explosions went off almost simultaneously. But the bus went up an hour later.
Yesterday, Hussain's family told of their horror at the teenager's involvement in the massacre. They said in a statement: "We are devastated over the events of the past few days. Hasib was a loving and normal young man who gave us no concern and we are having difficulty taking this in.
ARE THEY TALKING ABOUT THIS AL QAEDA???????