By Steve Kingstone
BBC News, Sao Paulo
Brazilian prosecutors have begun a formal probe into the fatal shooting of over 100 suspects by police in a wave of violence in the state of Sao Paulo.
More than 170 people died in clashes between gangs and police
Ten days ago members of the PCC, a crime faction controlled from within state prisons, began attacking police.
But as the number of attacks on police targets fell, there was a sharp rise in shootings by officers. Rights groups say innocent civilians were killed.
The police must now provide a full list of victims' names.
One hundred and nine people were shot dead by the police last week. Their names and the details of their deaths have not been made public.
The state government says that is out of respect for the victims' families.
But human rights groups are concerned at what they believe was an over-reaction by the police to earlier attacks on officers. They say the dead include innocent civilians.
Separately, members of the state medical council who have seen victims' bodies have told newspapers that some display signs of death by summary execution.
On Monday, state prosecutors formally requested a list of victims' names and for each death, a copy of the official police report.
Sao Paulo's civil and military police departments have been given until Thursday to comply.
In a statement, the prosecutor's office said there were concerns about the preservation of proof.
Responding to the human rights criticisms, the state governor, Claudio Lembo, acknowledged that here and there innocent civilians might have been killed, but he denied that officers had deliberately set out to take life.
With calm now restored in Sao Paulo, on Tuesday the focus will shift to Brasilia where members of Congress will question the lawyers of the man said to lead the PCC, the crime faction blamed for last week's violence.
The lawyers are alleged to have illegally bought audio recordings of an earlier parliamentary hearing in which secret details of prison transfers were discussed.
A sound technician has admitted selling the recordings for just under $90 (£48).