Three of the four terrorists — Mohammad Sidique Khan, 30, Shehzad Tanweer, 24, and Jermaine Lindsay, 19 — were captured by CCTV cameras travelling to King’s Cross on June 28. As on July 7, the men wore T-shirts, trainers and baseball caps; two had rucksacks slung. Police are scrutinising 80,000 pieces of footage from security cameras to discover how the three young Muslims spent almost four hours in the capital.

Officers are also studying 3,000 witness statements and 30,000 exhibits from the bomb scenes and 15 sites, including the bomb factory in Leeds, which took six weeks to search.

Another search at a landfill dump at Skelton Grange, West Yorkshire, continues. The police approach highlights the absence of any intelligence about the attacks.

On July 7, the three men who made the dummy run, accompanied by Hasib Hussain, 18, returned to King’s Cross where they separated to detonate four rucksack bombs and killed themselves and 52 Tube and bus passengers.

Deputy Assistant Commissioner Peter Clarke, head of the Metropolitan Police AntiTerrorist Branch, said that the scouting mission was indicative of “many months of planning”. That was further reflected in the bomb factory at Alexandra Grove, Leeds. Mr Clarke described the flat as “a carefully thought-out and effective bomb manufacturing facility”. He said: “Whoever made these bombs had done some very good research or had been well trained.

“It sounds clinical given the carnage that was caused that day, but these were very efficient explosives which left very little residue behind. They worked extremely effectively.”

He appealed for witnesses who may have seen the three in London on June 28. The footage shows the trio at 8.10am entering Luton railway station and buying tickets for the Thameslink service to King’s Cross. Those tickets have been found at addresses connected to the bombers.

Cameras at King’s Cross picked the men up at 8.52am and there was a further sighting at Baker Street around noon. Khan has a rucksack and Lindsay, wearing a New York Yankees baseball cap, carries a rucksack and a plastic bag. Tanweer, in a Puma T-shirt with his gelled hair swept back, is empty-handed. They were recorded at King’s Cross again at 12.50pm and took a train back to Luton where they appeared on camera at 1.40pm.

Mr Clarke said: “The obvious implication is that they were possibly conducting reconnaissance on that day. We know that is part of a terrorist’s methodology: to check timings, layout and security precautions. We are trying to reconstruct their movements as far as we can on that day. What we want to know is where else they went and did they meet anybody else while they were in London?”

Police outlined further details of the bombers’ movements on July 7. They believe Khan, Tanweer and Hussain left Leeds at 4am and drove to Luton in the hire car, a silver Nissan Micra. They had a substantial quantity of their explosives. The material, a compound known as HMTD, was stored in cool boxes with ice packs to keep it stable.

They arrived at Luton railway station at 6.51am and met Lindsay, who had been waiting for them in his car since shortly after 5am. The men packed the devices into rucksacks and caught the train, leaving behind in the hire car two bombs consisting of explosives packed into plastic bottles with fuses attached and packed around with nails. These were found in a rucksack beneath the front passenger seat. Another 14 potential bomb components, including cakes of high-explosive, were found in the boot.

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