Poch is alleged to have worked as a pilot at the Navy Mechanics School, which gained notoriety for being a torture centre during the war.
Velasco ordered that Poch be held in prison until Argentina puts in a formal request for his extradition, Iganacio Pelaez, Poch's lawyer, said.
Poch has said that he had no involvement with the deaths in Argentina, Pelaez said.
"He still doesn't understand anything," Pelaez told the Associated Press news agency.
"It's all a nightmare for him. He doesn't understand why he is here."
Poch currently works for Transavia, a buget airline that operates along tourist routes between the Netherlands and other European and North African cities.
About 13,000 people died in the war against dissidents during Argentina's period of military rule between 1976-1983, the country's government has estimated.
Human rights groups say the death toll is more likely to have approached 30,000.