GENEVA — Seif al-Islam el-Qaddafi, the son of Libya’s ousted dictator, should be turned over to the International Criminal Court to be tried on war crimes charges, the United Nations said on Tuesday, adding that he did not get a fair trial in Libya.

But the question is, who will hand him over?

A court in Tripoli, the Libyan capital, convicted Mr. Qaddafi in July 2015 and condemned him to death, but he was not in the court’s custody. Mr. Qaddafi had been detained by a militia in the northwestern city of Zintan, and took part in the proceedings only by video link; the militia refused to hand him over to the Tripoli authorities, citing security issues.

A year after the verdict, the commander of the militia announced that Mr. Qaddafi had been released under an amnesty decree issued by the Libyan government. Mr. Qaddafi has not been seen in public since, the United Nations said, and his status is unclear; he may still be held by the militia.

In the Tripoli trial, Mr. Qaddafi and 36 other defendants were charged with indiscriminate attacks on civilians and other crimes committed during the 2011 revolution that toppled Mr. Qaddafi’s father, Col. Muammar el-Qaddafi. Nine of the defendants were sentenced to death, including Mr. Qaddafi and Abdullah al-Senussi, his father’s intelligence chief.