By Tom Gibb
BBC News, Sao Paulo
The Brazilian government has opened up secret files dating from the military dictatorship between 1964 and 1985.
More than 1,200 boxes of documents are being made public
It follows a long campaign by human rights organisations and family members of those killed or disappeared.
But one rights group says some files containing crucial information about victims have been held back.
More than 400 left-wing activists and guerrillas are believed to have been killed under military rule, and more than 160 disappeared.
But this is far fewer than in neighbouring countries like Argentina and Chile.
Today, Brazil lags behind in terms of investigating military abuses.
'Too little, too late'
When left-wing President Lula da Silva was elected three years ago, many expected files from the military dictatorship to be opened up.
Instead, his defence minister claimed the army had destroyed all the files.
However, a leaked photograph was published showing a naked man in a prison cell with a story suggesting it was a well-known journalist murdered under military rule.
The defence minister resigned.
The newly-released documents are in 13 steel archives and more than 1,200 boxes.
But the Brazilian human rights group, Torture Never Again, says too little has been declassified and too late.
The group believes there are many more files still secret, which have direct information about those killed or disappeared and which could implicate officials still in office.
It accuses the government of continuing to cover up the past.