Underground inquiry still in the dark

The attacks

Three bombs exploded within 50 seconds of each other at 8.50am local time on underground trains heading south, east and west from London's King's Cross station. A fourth went off at 9.47am on a double-decker bus nearby.

Casualties

Fifty-six people, including the four bombers, were killed in the blasts. About 700 were wounded.

The bombs

The homemade peroxide-based explosives were made in a sophisticated "bomb factory" in Leeds, northern England. The bombs were carried in rucksacks and contained less than 4.5kg each of explosives. A car used by the bombers to travel to Luton on the day of the attack also had two nail bombs hidden in a rucksack underneath the passenger seat.

The bombers

Shehzad Tanweer, 22, blew up a train at Aldgate underground station; Mohammad Sidique Khan, 30, did the same at Edgware Road; Hasib Hussain, 18, carried the bomb that blew up a double-decker bus in Tavistock Square. Germaine Lindsay, a Jamaican-born convert to Islam who had been living in Aylesbury, northwest of London, died at Russell Square.

Dry run

Tanweer, Khan and Lindsay, were caught on CCTV cameras staging a dry run to the capital just over a week before the attacks, following the exact route used on the day of the attacks.

The hunt

Police have spoken to 3000 witnesses, examined more than 30,000 items, watched 80,000 surveillance recordings and searched 15 locations including a landfill site as big as 18 Olympic-sized swimming pools.

July 21

Detectives say four men tried to set off bombs on three underground trains and a bus in an identical plot two weeks later but their devices failed to explode. A fifth man is accused of dumping a suspected bomb in a west London park two days later. They are due to go on trial in September.

- REUTERS