The death of Libya's former leader Muammar Gaddafi "creates suspicions" of war crimes, says the chief prosecutor of the International Criminal Court.
Luis Moreno-Ocampo said the ICC was raising the concern with Libya's National Transitional Council (NTC).
Col Gaddafi was killed on 20 October after being caught by rebels in his home town of Sirte.
NTC officials initially said he died in crossfire, but promised to investigate following Western pressure.
"I think the way in which Mr Gaddafi was killed creates suspicions of... war crimes," Mr Moreno-Ocampo told reporters.
"I think that's a very important issue. We are raising this concern to the national authorities and they are preparing a plan to have a comprehensive strategy to investigate all these crimes."
Rebel fighters found Col Gaddafi hiding in a concrete drainage pipe after a long and bloody siege of the former leader's home city of Sirte.
He had gone into hiding in August, six months after the Libyan uprising began and five months after Nato intervened in the conflict.
Amateur videos taken at the time of his capture showed him injured but alive, surrounded by a frenzied crowd of jubilant rebel fighters.
He is hustled through the crowd and beaten to the ground on several occasions, before he disappears in the crush and the crackle of gunfire is heard.
His son Mutassim, captured alive with him, also died in the custody of rebel fighters.
The National Transitional Council initially said that Col Gaddafi had been killed in crossfire, but under pressure from Western allies it later promised to investigate how he and his son were killed.
The ICC has indicted another of Col Gaddafi's sons, Saif al-Islam, for alleged war crimes and he is in the custody of the Libyan authorities.
Mr Moreno-Ocampo has accepted that Saif al-Islam will be tried in Libya, not The Hague.