Argentine former police officer Mario Sandoval, who was arrested in France on Wednesday, is wanted for crimes against humanity, and torture in connection with the country's "dirty war."

Prosecutors believe Sandoval took part in the kidnapping, torture and murder of some 500 people, at a time when some 30,000 were "disappeared" by the 1976-83 dictatorship.

However, prosecutors based a long-running quest for his extradition on just one case -- that of architecture student Hernan Abriata, whose body has never been found.

Abriata was taken away from his parents' home in Buenos Aires on the night of October 30, 1976.

Answering a ring at the front door, they said they saw a man in military fatigues who introduced himself as "Sandoval, from Federal Coordination" -- a feared police unit linked to disappearances and torture.

Sandoval told them Abriata was wanted for questioning, under a "routine procedure," but they never saw their son again.

Abriata was taken to the Navy Higher School of Mechanics (ESMA) -- one of the dictatorship's main detention and torture centers where some 5,000 people are known to have died or disappeared. Some were thrown from planes into the River Plate.

Sandoval, 66, fled Argentina after the military junta fell in 1983 and built a new life in Paris, obtaining French nationality in 1997.

His citizenship does not prevent his extradition, however, as he was not French at the time of the alleged crimes.

Sandoval worked as a professor at the Sorbonne's Institute of Latin American Studies in Paris and the University of Marne-la-Vallee outside the French capital.

His colleagues at both schools called for him to be arrested when they recognized his picture during his legal battles.

Beatriz Cantarini de Abriata holds a portrait of her son Hernan, who is believed to have been the victim of the "butcher" of Argentina's dictatorship Mario Sandoval, who has been arrested in France
Beatriz Cantarini de Abriata holds a portrait of her son Hernan, who is believed to have been the victim of the "butcher" of Argentina's dictatorship Mario Sandoval, who has been arrested in France AFP / DANIEL GARCIA

In Argentina, he is known as the "butcher" of the dictatorship.

Sandoval has defended himself tooth and nail in the courts.

He unsuccessfully sued several French media organizations for defamation in 2008 after they published stories about his alleged role in the dictatorship.

After a long legal battle, the French government gave the go-ahead for Sandoval's extradition in August and finally moved to arrest him in eastern Paris on Wednesday.

Argentina has been seeking his extradition since 2012.

"He was a very strange guy, he did intelligence. He was the most intellectually prepared guy in the ESMA," one "dirty war" survivor, Alfredo Buzzalino, told prosecutors.

"If he could kill you, he killed you."

Carlos Loza, a friend of Abriata and a fellow detainee in ESMA, told a judge that Abriata was tortured several times.

The last time he saw Abriata "was between the 4th and 5th of January 1977," Loza said, adding that he was being "transferred" -- a euphemism for being taken away to be executed.

Argentina