French judicial authorities have opened an investigation for suspected involuntary manslaughter over the midair crash of two helicopters in Argentina last month that killed 10 people.

Paris prosecutor's office spokeswoman Agnes Thibault-Lecuivre said Friday's move marks a new step following a preliminary investigation that was opened shortly after the March 9 collision in a remote part of Argentina.

Under French law, the judicial order in essence formalizes the investigation and transfers control of it from the Paris prosecutor's office to a special investigating judge.

The eight French victims included swimmer Camille Muffat, boxer Alexis Vastine and sailor Florence Arthaud. They had been among the contestants in the reality TV show "Dropped."