Two years and one month after the Madrid train bombings the judge overseeing the inquiry is due to charge around 40 mainly Moroccan suspects with involvement in Spain's worst extremist attack.

Flowers and candles are placed in front of the Santa Eugenia train station near Madrid 10 March, to mark the second anniversary of the Madrid train bombings. Two years and one month after Spain's worst terrorist attack a judge is due to charge some 40 out of 116 mainly Moroccan suspects with involvement in the March 11, 2004 train bombings. [AFP]

Legal sources say judge Juan del Olmo will charge three men -- Jamal Zougam and Abdelmajid Bouchar from Morocco and Basel Ghayoun from Syria -- with actually carrying out the bombings which killed 191 people on four packed commuter trains on the morning of March 11, 2004.

Zougam and Ghayoun have both been identified by commuters on the trains, which were blown apart by 10 bombs. Around 1,9000 people were injured.

Bouchar was extradited from Serbia-Montenegro after escaping from an apartment in Leganes, south of Madrid, where seven of the suspected bombers blew themselves up during a police raid three weeks after the blasts.

A policeman died during the assault.

The investigation into the bombings has been painstaking, the dossier running to some 80,000 pages in 200 volumes.

The charge sheet itself is to run to more than 1,000 pages.

In all, 25 people suspected of taking part in the attacks are in prison -- one of them, Egyptian Rabei Osman, in Italy. A further 42 are on bail.

According to Spanish law, the suspects can be held for up to two years in detention without trial, a period which can be extended once.

The actual trial of those charged is due to start later this year or even early next year and last for around 12 months.

To date, only one person, a Spanish teenager nicknamed El Gitanillo (the little gypsy), has been sentenced in connection with the attacks.

The youngster was ordered to serve six years youth custody in November 2004 for handling the explosives used in the bombings. The material had been stolen from a disused mine in the northern region of Asturias.

The bombings turned Spanish politics upside down, producing a surprise general election defeat three days later for the incumbent conservative Popular Party.

The Popular Party (PP) initially insisted the attacks were the work of Basque separatists before evidence emerged pointing to Islamic extremists anggy at Spain's then support for the US-led invasion of Iraq.

Three days after the bombings the PP lost a general election to the Socialists of Jose Luis Rodriguez Zapatero, who had pledged before the ballot to pull Spain's troops out of Iraq.

In June 2005, a parliamentary committee of inquiry into the bombings criticised the then PP leader and prime minister, Jose Maria Aznar, for not taking the threat of Islamic extremism seriously and for blaming Basque separatist group ETA.

It also emerged last year that Spain's National Intelligence Centre (CNI) had warned the interior ministry that an attack by Islamic radicals could not be discounted.

Aznar has denied allegations that the Popular Party misled voters in the run-up to the general election by insisting the attack were the work of ETA, which the PP had vowed to crush.

The huge trial of the suspects will be pored over by those who lost loved ones in the bombings. Some victims' relatives and associations have expressed frustration with the slow progress of the investigations.

The hunt for DNA clues from the perpetrators and their accomplices has been complicated by the suicides of the seven suspects in the explosion in Leganes.

So investigators have laboriously pieced together what clues they have been able to glean from other sites where suspects are thought to have prepared the carnage.

Investigators have earmarked four main sites. They include a house just south east of Madrid where a total of 13 bombs were put together -- three did not explode during the attacks -- and the Alcala de Henares railway station, east of the capital, where the "trains of death" left for the city.

Prosecutors say the bombs were activated by mobile phones from a shop in Madrid where Zougam worked.

But no fingerprints or other evidence linking Zougam to the preparations have been discovered at any of these sites.