MADRID (AFP) - Spain's Supreme Court Thursday overturned the guilty verdicts on four of the 21 people convicted over the Madrid train bombings that killed 191 people in 2004. It also upheld a lower court's decision to acquit one of the alleged masterminds of the Al Qaeda-inspired attacks, Rabei Ousmane Sayed Ahmed, known as "Muhammad the Egyptian". And it handed down a four-year prison term to a Spaniard, Antonio Toro, who had been acquitted on charges of transporting explosives. The early morning bombings on four packed commuter trains on March 11, 2004 were the deadliest terror attacks in the West since the September 11, 2001 strikes against the US. On October 31 last year, Spain's anti-terrorist court convicted 21 people of involvement, and acquitted six others. The Supreme Court Thursday overturned the convictions of Basel Ghalyoun and Muhamad Almallah Dabas, both condemned to 12 years in prison for belonging to a terrorist group. It also cleared Abdelilah El Fadual El Akil, condemned to nine years for collaborating with a terrorist group, as well as Raul Gonzalez Pena, who had received five years for supplying explosives. But it rejected an appeal by prosecutors against the acquittal of "Muhammad the Egyptian". The Supreme Court Thursday also reduced the prison terms of others convicted, including Mahamed Larbi Ben Sellan, who saw his 12-year sentence for belonging to a terrorist group shortened to nine years, and Hassan El Haski, whose 15-year sentence on the same charge was cut to 14 years. A total of 28 defendants were on trial last year - 19 mostly North African Arabs living in Spain and nine Spaniards. The court in October had handed down the heaviest sentences to two Moroccans - Jamal Zougam and Othman el-Gnaoui - and a Spaniard, Jose Emilio Suarez Trashorras. They received around 40,000 years in prison each, although under Spanish law the maximum they can spend behind bars is 40 years. Zougam placed bombs aboard one of the four targeted trains, while el-Gnaoui and Trashorras were condemned respectively for supplying and transporting the explosives. The conservative government in power at the time initially blamed the armed Basque separatist group ETA for the attacks. But evidence quickly began to point to Islamic radicals angered over Madrid's decision to send troops to back the US-led war in Iraq. The Opposition Socialists scored a surprise victory in a general election three days after the bombings, aided by the perception that the ruling Popular Party had tried to cover up evidence that Islamic radicals were behind the bombings.