An appeal hearing against the conviction of a former Bosnian Serb general involved in the Srebrenica massacre has begun at the Hague.
Krstic was originally sentenced to 46 years
Two years' ago Radislav Krstic received a 46-year sentence for his involvement in the 1995 killing of 7,000 Muslims.
Two other Bosnian Serb army officers who pleaded guilty to crimes at Srebrenica are due to testify.
The prosecution is seeking a life sentence for Krstic, while the defence wants the genocide conviction quashed.
The Srebrenica massacre is considered Europe's worst atrocity since World War II.
Prosecutor Mathias Marcussen told the International War Crimes Tribunal that the 46-year sentence did not reflect the gravity of the crime.
"When an accused is convicted and found guilty of 8,000 murders and the forceable transfer of 20,000-25,000, only a life sentence is appropriate," he said.
He added that Krstic should have foreseen that "people would be killed, raped,
"Without him, these crimes would not have been committed," he said.
The defence team for Krstic, 58, is expected to respond later on Wednesday and present its own case on Thursday.
His lawyers claim he did not know his soldiers were killing thousands of Muslims.
But the defence is expected to fight against new evidence at the appeal - the testimony of two of Krstic's fellow officers, Momir Nikolic and Dragan Obrenovic.
They pleaded guilty in May to persecution and admitted they knew of the executions.
The BBC's Geraldine Coughlan, at The Hague, says this could be an important element for prosecutors, who claim Krstic was also fully aware of what his subordinates were doing but did nothing to stop the slaughter or punish those responsible.
Judges at the original trial in 2001 ruled that Krstic had "agreed to evil" as commander of the Drina Corps and had overseen the massacre.