"This is excellent news, because Operation Colombo was also a case in which General Pinochet's immunity from prosecution was stripped and - given the number of victims - is an emblematic case," Sergio Laurenti, executive director of Amnesty International in Chile, told Reuters news agency.
"But it is important that the police now furnish the necessary information to enable the courts to proceed," he said.
"There is a lack of co-operation from the armed forces and security forces."
Also on Monday Michelle Bachelet, the Chilean president, attended a ceremony to inaugurate a human rights memorial in the town of Paine near the capital, Santiago, to commemorate 70 people who were either executed or detained and later "disappeared" in the town during Pinochet's rule.
"Some cases are advancing more than others ... but I hope none is closed until all those responsible are found"
Carlos Maldonado, Chile justice minister
According to court documents, Pinochet's secret service, known as Dina, seized the 119 activists and Pinochet opponents in July 1975 and killed them.
However in a bid to counter media reports about repression in the country, the agency claimed falsely that they had either left the country or died fighting different opposition factions.
Investigators later accounted for the bodies or whereabouts of many of the dead, but at least 42 were never found and Montiglio said they should still be considered kidnapping victims.
Among those being sought is the former head of Dina, Manuel Contreras, who is already in prison for other abuses.
Pinochet himself was briefly indicted on kidnapping charges in the same case, before his death in December 2006.
During his military government's rule, from 1973 until 1990, about 3,000 people died or disappeared, 28,000 were tortured and about 200,000 fled into exile.
"All advances in human rights cases are important," justice minister Carlos Maldonado said on Monday.
"Some cases are advancing more than others ... but I hope none is closed until all those responsible are found."