Video footage of mutilated victims of Sierra Leone rebels has been shown at the war crimes trial of Liberia's former President Charles Taylor.
Charles Taylor denies responsibility for atrocities
Mr Taylor - who is accused of trading weapons for diamonds - showed no emotion as the first witness, an expert on "blood diamonds", gave evidence.
The delayed trial has resumed at The Hague after a six-month delay.
Mr Taylor is the first African former head of state to face an international war crimes court and faces 11 charges.
He denies responsibility for atrocities committed by rebels during the civil war in neighbouring Sierra Leone.
Video of a Sierra Leonean diamond miner was shown to the court, in which he described how his hands were hacked off by laughing Revolutionary United Front (RUF) rebels who later burned down his house, killing his wife and children.
The case against Mr Taylor centres on allegations that diamonds illegally mined by rebels in Sierra Leone were exported from Liberia with Mr Taylor's co-operation, and the proceeds from their sale used to buy weapons for the rebels.
Witness Ian Smillie, who wrote a report for the United Nations on conflict - or "blood" - diamonds, said the former RUF rebels used brutality to frighten people away from diamond fields that earned them up to $125m (£63m) a year.
He said figures showed that during the war in Sierra Leone, Liberia exported far more diamonds than it could have produced itself.
He said that when he met Mr Taylor in 2000, the former president had told him it was "highly probable" that the former RUF rebels were dealing in diamonds, and that some of them might have been going through Liberia.
"But, he said this was not official, and he didn't know anything about it," Mr Smillie told the court. "He said the borders were very porous and he had no control over this."
Mr Taylor's defence objected to some of Mr Smillie's testimony as hearsay, but most of it was accepted by the court.
The trial opened in June last year but proceedings were postponed after Mr Taylor fired his defence lawyer and boycotted the opening of the trial.
He now has a new defence team - a senior British lawyer, who is being paid for by the court, as Mr Taylor says he cannot afford it himself.
The BBC's Mark Doyle in The Hague says this will surprise many people in Liberia, who claim he made lots of money by selling timber and diamonds.
Mr Taylor is accused of responsibility for the actions of Revolutionary United Front rebels during the 1991-2001 civil war in Sierra Leone, which included unlawful killings, sexual slavery, use of child soldiers and looting.
RUF fighters were also notorious for hacking off the arms and legs of the civilian population with machetes.
As the first international criminal prosecution against a former African ruler accused of misdeeds, the case is of crucial importance, our correspondent says.
Mr Taylor has pleaded not guilty to all 11 counts of war crimes and crimes against humanity.
The prosecution will also be calling a Liberian witness who is said to have belonged to Mr Taylor's inner circle.
Both witnesses are protected, which means their names have not been revealed.
In all, the prosecution intends to call 144 witnesses, though only half are likely to appear in person.
The trial is expected to last about 18 months.
It is being held in The Hague for fear that staging it in Sierra Leone might lead to fresh unrest there.
If convicted, the UK has offered to jail him - again in case his presence in West Africa led to instability.