Gaddafi is the first person to be accused by the International Criminal Court chief prosecutor of "enforced disappearance", a phenomenon made notorious by the Argentinean and Chilean juntas of the 1970s and 80s.
Thousands of political opponents and trade unionists disappeared but no bodies were found, so no murder or kidnap could be proved.
ICC chief prosecutor Luis Moreno Ocampo, who made his name leading the case against junta leaders in his native Argentina, said he now has evidence that in Libya "the behaviour is abduction, torture and disappearance. This is a tool to establish fear."
The ICC judges are to announce within days whether they agree to crimes against humanity charges against Gaddafi, who would join Sudan's President Omar al-Bashir on the international wanted list.
Yugoslav leader Slobodan Milosevic died before his genocide trial was completed.
"This is different from Bashir in Darfur where it was killings and rape or Milosevic," Moreno-Ocampo told AFP.
Gaddafi's son Seif al-Islam and intelligence head Abdullah Senussi are also accused by the prosecutor of being "criminally responsible for the killings, arrests, detentions, disappearances and acts of ill-treatment against unarmed demonstrators and alleged dissidents."
"It is being used for the first time because of the circumstances, but it is important that this is established as a crime against humanity," Moreno-Ocampo said.
During the trials of the Argentinian junta there was no crime of disappearance. But two French nuns were among those who disappeared and France helped provide the evidence that convicted navy officer Alfredo Astiz, the so-called "Blonde Angel of Death," for murders including the nuns.
Moreno-Ocampo said he was "grateful" for France's help and France and Argentina are now leading efforts to get countries to ratify the 2006 International Convention for the Protection of All Persons from Enforced Disappearance.
Eighty-eight states have signed the convention but as of this month, only about 25 have ratified the treaty -- which means that they must make enforced disappearance a criminal offence and bring to justice those responsible for such cases.
Among countries that have refused to sign the convention are the United States, European nations such as Britain, and other western allies. All raised technical objections.
But Iraq became the 20th country to ratify the convention in December so that it could come into force.
"If the charges against Gaddafi encourage other countries to sign up for the convention then that is a good thing," said Aisling Reidy, a senior legal advisor for Human Rights Watch in New York.
"Ratifications have definitely been slow and it is a sad fact that disappearances are continuing all the time -- from China to Chechnya."
Reidy said there had been a "worrying" number of Chinese dissidents, journalists and lawyers go missing in recent months as the authorities launch a crackdown, fearing their own Arab Spring style uprising.
And the scars from "enforced disappearances" pass from generation to generation.
At a recent discussion on the treaty at the UN headquarters was Estela Carlotto, whose pregnant daughter was among the thousands of victims of the Argentinian junta.
Carlotto was once the head of the Mothers of Plaza Del Mayo who staged regular protests in Buenos Aires demanding news of their children.
After being given proof of the brutal murder of her daughter she became president of the Grandmothers of Plaza Del Mayo, now campaigning to find out what happened to her grandchild -- one of 500 born in military captivity and given or sold to adoptive parents.