Three of the 24 suspects face jail terms of 74,377 years for their alleged involvement in preparing the 11 September 2001 attacks on the US in which some 3000 people were killed.
Imad Eddin Barakat Yarkas, alias Abu Dahdah, Driss Chebli and Ghasoub Al Abrash, alias Abu Musab, are accused of helping to prepare the attacks following a meeting in July 2001 in Spain believed to have been attended by Mohamed Atta, the suspected ringleader of the hijackers who attacked the World Trade Centre in New York.
According to public prosecutor Pedro Rubira, the meeting "probably determined the date of the attacks on the United States".
Abu Dahdah, sitting with 15 co-defendants behind a glass screen, insisted the whole case was a farce.
Speaking of al-Qaida leader Osama bin Laden, he said: "I know absolutely nothing of this man. I condemn what happened [on September 11]."
"The killings are something we cannot accept," he said of the attacks as he availed himself of the right under Spanish law to speak at the end of the proceedings.
The verdict is expected in the second half of September.
Aljazeera's Taysir Alluni says he
is innocent of the charges
Abu Dahdah said accusations he had headed a "soldiers of Allah" group of Islamic extremists were "a myth - totally false".
He said that Islam "clearly says that killing children, women, elderly people is wrong, as is bringing down buildings".
Eight of the men have been released from custody since the trial started, but must still report daily to the police.
The eight sat on Tuesday in open court and included Aljazeera reporter Taysir Alluni, who told in testimony in May how he interviewed bin Laden weeks after the attacks.
Alluni reiterated that he was innocent.
"They are looking for an exemplary punishment for us [the Muslim community]," said Alluni, who added that hundreds of relatives and friends had "endured so much suffering" given the weight of suspicion over the accused.
Defence lawyers had earlier poured scorn on the investigation which led to the trial, which opened on 22 April and has heard from 107 witnesses, including Jamel Zougam, an alleged Moroccan acquaintance of Abu Dahdah.
Zougam, held as a prime suspect over the Madrid train bombings in March last year, appeared in court a month ago to say that while he vaguely knew Abu Dahdah, it was only because they had met shopping in the Lavapies district of Madrid, which has a large Arab population.
"They are looking for an exemplary punishment for us [the Muslim community]"
Luis Gonzalez Galan, alias Yusuf Galan, the only Spanish-born suspect, also said he was innocent.
"I have never been a terrorist. I oppose all terrorist violence which brings death and bloodshed," added Galan, who said he believed in justice and peace.
The trial has spent 53 sessions trying to establish the men's guilt and court officials said 130 hours and 39 minutes of real time evidence has been collated on 18 DVDs.
In addition, Spain has contacted six countries - Belgium, Germany, Kuwait, Syria, the United Kingdom and the United States - for further information.
Kuwait and Syria have yet to respond, court sources said, while the other four have been investigating.
Defence lawyers said on Tuesday the case against their clients was not proven.
"Unless it is absolutely certain that the prosecution case stands, then they must be acquitted," said a lawyer for four of the men, who denounced the "doubts and more doubts" and the "suspicions and more suspicions" but, in his view, little concrete substance for conviction.