El Salvador's transparency authority called on the army Wednesday to open its archives as part of a new investigation into an ambush which killed four Dutch journalists in 1982.
TV journalists Koos Koster, Jan Corenlius Kuiper, Hans ter Laag and Johannes Willemsen were covering El Salvador's civil war when they were killed with rebels accompanying them in Chalatenango, around 50 miles (80 kilometers) north of the capital San Salvador.
The Salvadoran Institute for Access to Public Information (IAIP) has given the defense ministry 30 days to hand over documents detailing military operations at the time of the ambush.
The IAIP said it was looking for precise information on helicopter flight plans as well as the identities of crew members arriving or departing from the 4th Infantry Brigade headquarters at El Paraiso.
Nobody has ever been prosecuted for the killings.
In 1993, a United Nations Truth Commission investigation concluded the journalists were deliberately killed in an ambush set up on the orders of 4th Infantry Brigade Commander, Colonel Mario Reyes Mena along with other officers.