(CNN) -- It has only happened a few times in history. This time the legal anomaly is taking place in Cambodia. It's known as Case Number 2, a joint trial for the remaining top leadership of the now defunct Khmer Rouge government for crimes against humanity, murder and torture.
There are four defendants in the case -- Ieng Sary, the former Khmer Rouge foreign minister; his wife, Ieng Thirith, former social affairs minister for the regime; Khieu Samphon, the nominal head of state; and Nuon Chea, the prime minister also known as Brother Number 2. The head of the Khmer Rouge, Pol Pot, was known as Brother number 1, but he died in 1998, long before the U.N.-backed court came into existence.
For the first time the defendants all appeared in court together because Monday was the start of their trial.
All the defendants are over the age of 77. Only a few minutes into the proceeding, 84-year-old Nuon Chea through his attorney asked the court to allow him to wear his warm hat to keep warm in the air-conditioning. He also asked if he could keep on his large dark glasses to avoid the glare of the court's lights.
The court agreed. The physical state of the four does not square with the crimes they're accused of. They are charged with devising the policies that led to the murders of hundreds of thousand of people, torture, genocide, and war crimes just to name a few.
It has been more than 30 years since they were in power but on the first day of this historic trial defendant Nuon Chea takes off his glasses to inject a strong opinion about the court proceedings:
"I am not happy with this hearing and I would like to make uh to allow my co-counsels to explain the reasons behind this."
His co-counsel, Michiel Pestman, argued the court had denied hearing from 300 of his witnesses and gone against every argument they made.
"Our main objections were against the judicial investigation carried out by the investigative judges that was so unfair and so harmful to the rights of our client, Noun Chea, that we think these proceedings should be terminated," Pestman said.
The court said it would take it into consideration and make a decision.
The court began hearing other motions. The defense for Ieng Sary said the case against him should be dismissed, on grounds of double jeopardy -- a defendant cannot be tried twice for the same crime.
When the Vietnamese drove out the Khmer Rouge they quickly put Ieng on trial and convicted him in absentia in 1979. When he defected from what remained of the broken Khmer Rouge regime in 1996 the Cambodian king pardoned him.
Again the judges agreed to look at the legal merits of the argument.
They are not the only ones watching this process very closely. Some have accused the court of not going far enough in its investigations into other potential cases. The International prosecutor wants to try several more defendants in cases 003 and 004, but the government of Cambodia wants case 002 to be the end of the Khmer Rouge trials.
"A lot of it at this stage isn't very public, so there's a lot of rumor about how its happening but once we get to the closing orders that decided whether to proceed or not to proceed with the case then there will be appeals where I think people can judge the process for themselves," said Steven Rapp, U.S. ambassador-at-large for war crimes issues. He arrived at the court to observe and said the court appeared to be doing its legal duty.
To give you an idea of just how important this trial is to the Cambodian people, every single seat in the gallery was taken -- all 500 of them.
Thousands more people from all over the country have signed up to see the trial.
"I want to know how the court proceedings work," said 79-year-old Pem Song, a Cambodian monk.
He said he traveled 250 kilometers just to spend one day here along with several others from his monastery. Pem remembers the days of the Khmer Rouge, how they took him into custody and forced him into farm labor.
"They killed so many of people, so they have to be punished," he said.
For that to happen, the court must do what it has been commissioned to do to -- investigate and find the truth about those who were most responsible for the Khmer Rouge's cruel and deadly practices.
Tim Schwarz contributed to this report.