The Brazilian state of Sao Paulo should conduct a "prompt and impartial investigation" into cases of unlawful killings by police, Human Rights Watch said Monday.
In a letter to Governor Geraldo Alckmin and Attorney General Marcio Rosa, the group detailed findings that extrajudicial killings by state police officers were being misreported and covered up as deaths from shootouts.
"Police take the corpses of their execution victims to hospitals in order to destroy crime scene evidence," the letter said.
The New York-based group also noted that "in some cases police continue to plant evidence on victims following police extrajudicial executions."
The letter, signed by the head of HRW's Americas division, Jose Miguel Vivanco, demanded that officials "make certain that police officers who break the law are brought to justice."
HRW says it examined 22 police killings from 2010 through 2012 and that evidence cast "serious doubt" on police claims that the deaths were justified.
In 20 of those cases, evidence pointed to the removal of bodies from crime scenes and delivery to hospitals for "rescue" attempts, HRW said.
The organization did acknowledge that police faced "real threats of violence" and that some killings were the result of legitimate use of force.
HRW called for resolutions to be respected barring the removal of bodies from the scene except in rare occasions. It also promoted a protocol for analyzing victims' clothing and the immediate notification of prosecutors over police killings.
A 2009 HRW report documented 16 Sao Paulo and 35 Rio de Janeiro cases in which police "appeared to have executed" individuals and then reported their deaths as the result of shootouts.
The state of Sao Paulo, home to 41 million people, has reduced violence in recent years and is now one of the safest in Brazil.
Nonetheless, it has faced waves of violence and police have been repeatedly accused of excessive use of force.