Former Interior Minister Sam Hinga Norman and two other leaders of the feared pro-government Kamajor militia are accused of crimes ranging from human sacrifice and cannibalism to recruiting child soldiers during the decade-long war.
In the capital city of Freetown on Thursday, the prosecution told a packed courtroom that witnesses would testify that Kamajor fighters paraded severed heads and ate the roasted flesh and intestines of their victims.
It said the three defendants, who have pleaded not guilty, were each personally liable for crimes carried out under their orders "as if they committed each and every crime themselves".
The war, in which 50,000 people were killed, shocked the world with its images of mutilated civilians and underage, drugged-up fighters carrying out atrocities.
"The ghosts of thousands of murdered dead stand among us. They cry out for a fair and transparent trial - to let the world know what took place here, here in Sierra Leone," US prosecutor David Crane said in his opening statement.
"The ghosts of thousands of murdered dead stand among us. They cry out for a fair and transparent trial - to let the world know what took place here in Sierra Leone"
As Crane spoke, Norman - the most senior government official to stand trial and a close associate of President Ahmad Tejan Kabbah - took notes, occasionally looking up to meet the prosecutor's eyes, a smile on his face.
Later, Norman said he now wanted to conduct his own defence, prompting the judge to adjourn the trial until next Tuesday.
Mix of judges
Sierra Leone's special war crimes court was set up to try those bearing the greatest responsibility for crimes committed during the conflict, declared over in 2002 after a huge UN peacekeeping force disarmed some 47,000 fighters.
It is the first of its kind to try suspects in the country where the crimes were committed and to be presided over by a mixture of UN-appointed and local judges.
"The Special Court sees itself and will continue to function as an important instrument of global justice and world peace," said court president Justice Emmanuel Olayinka Ayoola.
If successful, the model may be used for judicial proceedings in other parts of the world, such as the trial of former Iraqi President Saddam Hussein, court officials say.
The court's early days have been far from smooth and many victims in the dirt-poor former British colony say the outcome of the trial will make little difference to their lives.
A UN soldier guards the special
courthouse in Freetown
Top suspects among the 13 it has indicted so far have either died or fled into exile, and the court has twice had to replace its president after accusations of bias.
Former Liberian President Charles Taylor, indicted by the court for rape, murder, enslavement and pillage among other charges and seen as the mastermind behind a web of conflicts in West Africa, is living in exile in Nigeria.
Crane says he is confident Taylor will eventually be tried, but Nigeria has said it will not hand him over to the court.
Foday Sankoh, whose rebel Revolutionary United Front (RUF) became notorious for hacking off civilians' limbs, died in custody last year. Two other key suspects have been killed while at large.
The trial of the remaining RUF suspects is due next month. Members of a former military junta are also to stand trial.