The defendants - Issa Sesay, Morris Kallon and Augustine Gbao - were each personally liable for the crimes carried out under their command as they fought for control of the country's diamond mines in Sierra Leone's 10-year civil war, the prosecution said.
The prosecutors are accusing them of having killed, raped and mutilated their victims, and carving initials into the chests of child soldiers forced into battle when they were working for the Armed Forces Revolutionary Council (AFRC) and Revolutionary United Front (RUF).
"AFRC/RUF physically mutilated men, women and children, including amputating hands, feet, breasts, buttocks, lips, ears, noses, genitalia and carving AFRC or RUF on their bodies," US prosecutor David Crane told the country's UN-backed war crimes court in his opening statement on Monday.
"Children will come before you and testify in effect, 'I killed people. I'm sorry, I didn't mean it'," he said.
Fighting for control
The defence, representing the senior members of the rebel AFRC and RUF, was to set out its case later in the day.
"Children will come before you and
testify in effect,
'I killed people. I'm
sorry, I didn't mean it"
Sierra Leone's war killed 50,000 people and shocked the world with images of mutilated civilians and drugged up young militia.
It was declared over in 2002 after a UN peacekeeping force disarmed some 47,000 fighters.
The court in the West African country's sprawling capital was set up to bring to justice those bearing the greatest responsibility for atrocities. It is the first of its kind to try suspects in the country where the crimes were committed.
Crane said one witness would testify that he and his children were forced to watch while his wife was raped by eight different RUF rebels before the last one stabbed her to death with a bayonet.
"Why does he recall there being eight rapists, he will be asked? Because the witness had to count out loud the number as they tore into his wife," Crane said.
Another witness would testify that he was tied up in chains and forced at gunpoint to mine diamonds for the RUF for 12 hours at a time with no food.
Those who became too ill or weak were shot by RUF-trained children as young as 11-years old.
Two top suspects wanted by the court are now out of its reach. RUF leader Foday Sankoh died in custody last year and former Liberian President Charles Taylor, charged with backing the rebels, remains at-large and lives in Nigeria.
The court's first case began last month with three suspects - former Interior Minister Sam Hinga Norman and two other leaders of the feared pro-government Kamajor militia - facing charges of crimes against humanity.