The U.N. said Saif al-Islam Gaddafi, who was sentenced to death in absentia, should instead have his trial conducted at the International Criminal Court (ICC).
Since his father’s toppling in 2011, Saif has been held in Zintan, a mountainous western region, by one of the factions that began contending for power after Gaddafi was killed.
The 44-year-old was sentenced to death in 2015 by a Tripoli court for war crimes, including killing protesters during the revolution.
Zintani forces however refused to hand him over, saying they did not trust Tripoli to guarantee he does not escape.
The proceedings “fell short of international norms and standards for fair trial and also breached Libyan law in some respects”, a U.N. report said.
“No prosecution witnesses were called to testify in court, undermining the defendants’ ability to challenge evidence.” it added.
Saif, former intelligence chief Abdullah al-Senussi and former Prime Minister Al-Baghdadi a-Mahmoudi were among nine defendants sentenced to death by firing squad.