Three Britons went on trial Thursday on charges that they helped homicide bombers plan the 2005 attacks on London's transit network that killed 52 commuters.

Prosecutors say Waheed Ali, 24; Sadeer Saleem, 27; and Mohammed Shakil, 31, helped four bombers plan the July 7, 2005, attacks on three subway trains and a bus.

Prosecution lawyers, opening their case at Kingston Crown Court in London, said the three helped the bombers scout out possible targets for the attacks. Among the sites they visited were the Natural History Museum, the London Eye and the London Aquarium.

Lawyer Neil Flewitt said they also visited sites that "bore a striking similarity" to locations where Mohammed Siddique Khan, Shehzad Tanweer, Jermaine Lindsay and Hasib Hussain detonated bombs.

The three men acknowledge knowing the July 7 bombers but say they were not aware of the bomb plot. They say their trip from Leeds to London in December 2004 was a social visit.

Jurors were shown previously unseen video footage of the moment two of the bombs went off. One clip showed a blinding flash and a cloud of dust as Tanweer exploded his device near Aldgate subway station, killing seven people and himself. Another showed bystanders thrown to the ground when Hussain detonated a knapsack bomb on a bus near London's Tavistock Square. He and 13 other people died.

Family members of several victims watched from the court's public gallery, others from a special room set up within the courthouse.