A Spanish judge is expected to charge about 30 people with involvement in the 2004 Madrid train bombings tomorrow, completing a two-year investigation into attacks which left 191 people dead.
Judge Juan del Olmo will take steps toward a trial that probably won't start before early next year, judicial sources said.
Some 116 people have been named as suspects in the March 2004 attacks, in which bombs packed in sports bags exploded on four crowded commuter trains. Twenty-five people are already behind bars.
Del Olmo's report, which runs to more than 1,000 pages, will detail charges against the suspects.
The case is unprecedented in Spain in terms of bloodshed and complexity, and the trial could last 10 months because so many defendants and lawyers are involved, a lawyer said.
No venue for the trial has been named, but accommodation will be needed for hundreds of people including the accused, lawyers, court officials, police, journalists and members of public.
Before the case gets to trial it must pass through an initial preparatory period, but the High Court judge's report will be the main basis for the proceedings, legal experts say.
The March 11 bombs injured more than 2,000 people and traumatised Spain, already worn down by years of bombings and shootings by Basque guerrilla group ETA, which last month declared a permanent ceasefire.
Prosecutors say the 10 train bombs were activated by mobile phones that were traced to a shop in central Madrid, run by one of two main suspects.
Seven suspected bombers blew themselves up three weeks after the attack when police surrounded their apartment building in southern Madrid. Another fled Spain and died fighting in Iraq.