REUTERS - The last military president in Argentina's 1976-1983 dictatorship went on trial on Monday in a makeshift courtroom in a sports arena on charges of kidnapping, torture and murder of 56 people in a concentration camp.

Frail-looking Reynaldo Bignone, 81, a former general who ruled Argentina in 1982-1983, and seven other former military and police officers faced a three-judge panel on charges including the ordering of beatings, waterboardings and electrocutions at the Campo de Mayo army base.

Waterboarding is a form of simulated drowning widely considered torture.

Hundreds of people, including numerous relatives of the victims, turned out for the start of the trial, held in an indoor soccer arena in a Buenos Aires suburb because the local courthouse was not big enough to house the large number of people who wanted to attend the proceedings.

According to a government report, more than 11,000 people died or disappeared during Argentina's "Dirty War," a crackdown on leftists and other opponents of the military regime. Human rights groups say the number is closer to 30,000.

"This is a historic trial in the search for truth for the all of those who disappeared," Alcira Rios, a lawyer for relatives of one of the victims, told Reuters. "We have to say no to impunity. We owe it to our Argentine society."

Bignone rocked back and forth in his chair as the charges against him were read in court. He and the other defendants could face up to life in prison if convicted in a trial that could last up to five months.

More than 130 witnesses are expected to be called to testify against the elderly defendants, starting next week.

Also standing trial are former generals Santiago Omar Riveros, Eugenio Guanabens Perello and Fernando Exequiel Verplaetsen and former colonels Jorge Osvaldo Garcia, Carlos Alberto Tepedino and Eduardo Alfredo Esposito. Former police officer German Montenegro also went on trial.

During the trial's opening day, Verplaetsen was removed from the proceedings due to illness.

'They have committed genocide'

The accused "look like old men but they have committed genocide," Taty Almeida, a member of Mothers of Plaza de Mayo, a human rights group, said in an interview in the courtroom during a break in the proceedings.

Almeida's son, Alejandro Martinez, was a 20-year-old medical student in 1975 when he was kidnapped and murdered by the military. "When I see them there I feel repulsed but I also feel a great deal of achievement because they're being put on trial," Taty Almeida added.

Bignone, who is currently living under house arrest, was the last of four military de facto presidents in Argentina during the dictatorship.

He handed over the presidency to Raul Alfonsin, the country's first democratically elected leader after the dictatorship ended in 1983, as the military junta lost popularity over a deep economic crisis and a humiliating defeat in the war against Britain for the Falkland Islands.

In 2005, Argentina's Supreme Court, at the urging of then-President Nestor Kirchner, struck down two amnesty laws that shielded hundreds of former officers from charges of human rights abuses during the dictatorship. Since then, several people have been convicted of crimes and sentenced to prison.