A prosecutor on Monday accused three British Muslims of scouting out potential targets on behalf of homicide bombers who killed 52 commuters on London's transit system in 2005.

The three defendants denied the charges, pleading not guilty in front of jurors at London's Kingston Crown Court.

Waheed Ali, 25, Sadeer Saleem, 28, and Mohammed Shakil, 32 are being retried on a charge of conspiring to cause explosions with the bombers who blew themselves up aboard three subway trains and a bus on July 7, 2005.

Prosecution lawyer Neil Flewitt said in opening statements Monday that the three defendants had "conducted hostile reconnaissance of potential targets" during a visit to London seven months before the transit attacks.

The 2005 attacks were the deadliest on London since World War II, killing 52 commuters as well as the four homicide bombers — Mohammed Siddique Khan, Shehzad Tanweer, Jermaine Lindsay and Hasib Hussain.

Prosecutors said the three men on trial had traveled with Hussain on Dec. 16, 2004, from their northern English home town of Leeds to London, where they visited tourist sights, including the London Eye Ferris wheel, the Natural History Museum and the London Aquarium.

Flewitt said the two-day visit was a reconnaissance trip, "an important first step in what was, by then, a settled plan to cause explosions in the U.K."

He said the defendants did not take part directly in the attacks but helped the bombers prepare "an appalling act of terrorism."

Flewitt said the three men "were part of a plot that led ultimately and tragically to the events of the 7th July 2005."

He said the defendants shared the "radical ideology" of the bombers, who left videotaped messages in which they claimed to be motivated by Britain's involvement in the invasion of Iraq and other perceived attacks on the Muslim world.

The prosecution said the suspects' computers contained evidence of searches for sites related to the Taliban and al-Qaida. Flewitt said the defendants had attended meetings at the Iqra Bookshop in Leeds, where the bombers also gathered.

The defendants — the only people charged over the attacks — have acknowledged knowing the bombers, but said they were not aware of the bomb plot. They have said the trip to London was a social outing.

The prosecution claims the men had extensive links with the bombers and other alleged extremists.

Flewitt said Shakil attended a training camp in Pakistan in 2003 with Siddique Khan, the ringleader of the July 7 bomb plot. He said the men used machine guns, rocket-propelled grenade launchers and AK47 assault rifles and "appeared confident and experienced in their use of weapons."

Flewitt told the jury it would later hear evidence about the Pakistan trip from Mohammed Junaid Babar, a one-time al-Qaida operative turned police informer who is awaiting sentencing in the United States for terrorist offenses.

Other evidence comes from surveillance of a suspect identified only as Ausman, who was being watched by British authorities in 2004 when he met with two of the bombers and Ali.

The defendants are being tried a second time, after the jury at their first trial last year failed to reach a verdict. All three face a maximum life sentence if convicted.

Ali and Shakil also deny a second charge of conspiring to attend a terrorist training camp in Pakistan. They were arrested at Manchester airport on March 22, 2007, as they prepared to fly to Pakistan. Saleem was arrested in Leeds the same day.

Flewitt asked the jury to make a "calm and dispassionate assessment" of the evidence and not be swayed by their "understandable disgust" toward the July 7 bombers.

The trial is expected to last three months.