Feb 11 (Reuters) - Twenty-nine people charged in connection with the Madrid train bombings that killed 191 people go on trial on Feb. 15. Following are some of the main facts about the March 11, 2004, attacks:

WHAT HAPPENED: Ten bombs hidden in sports bags exploded on four packed commuter trains between 7:37 and 7:40 a.m.. One train was at Madrid's main Atocha station. Another was 500 metres away. The other two were at stations on a line into Madrid.

The bombs were set off by mobile phones.

WHO DID IT: Islamist militants, mostly Moroccans. A video message said the attacks were revenge for Spain sending troops to Iraq and Afghanistan. The judge investigating the case said the attack was inspired by, but not ordered by, al Qaeda.

Nine Spaniards have been charged with supplying dynamite to make the bombs.

The then-ruling conservative party first pinned the blame on ETA and some right-wing media and politicians have continued to try and link the Basque separatist group with the Islamists. The state prosecutor has ruled out any link.

VICTIMS: 191 people were killed, almost 2,000 people were injured.

WHAT HAPPENED NEXT POLITICALLY: Spain held a general election three days later and voters turned out in force to vote out the conservative Popular Party, which had backed the U.S.-led war in Iraq.

The new Socialist Prime Minister Jose Luis Rodriguez Zapatero won the election and quickly fulfilled an election pledge to withdraw Spanish troops from Iraq. Spain still has soldiers in Afghanistan.

WHAT HAPPENED NEXT WITH THE BOMBERS: On April 2, Spanish police found another bomb on a high-speed railway line between Madrid and Seville. No one was hurt.

On April 3, seven prime suspects blew themselves up in an apartment block when they found themselves surrounded by police. One policeman was killed in the blast.

WHAT IT COST: The judge who investigated the attacks said the explosives, mobile phones and accommodation cost the bombers about 55,000 euros ($71,460), some of it raised by selling drugs. Some materials, including cars, were stolen.

The group had up to 1.5 million euros' worth of hashish and ecstasy they could have sold to raise more cash, the judge said.

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