Families blame police in brutal deaths

• Police say four young men were killed in a shootout after a chase in a stolen car in September


• After receiving gruesome photographs, families suspect the young men were tortured


• State officials have declined interview requests but say they are investigating the deaths


• Sao Paulo public defender has asked U.N. to investigate the killings

Sao Paulo, Brazil (CNN) -- The grave is in a cemetery on the outskirts of Sao Paulo, marked only by a number. The families haven't yet added the names of the two young men who were recently buried there together.

Paulo Pinheiro da Silva, 21, and Luan da Silva, 18, (no relation) and two others, also teenagers, were shot to death by police in September.

According to police, the four were killed in a shootout after being chased for more than 10 kilometers (6.2 miles) in a stolen car. Authorities haven't provided further details.

Family and friends say the youths were last seen at a party in the poor suburb where they grew up. Some witnesses say they saw police detain them when they went for a walk outside. The next day, their desperate families learned they could find them in the morgue.

Tereza Pinheiro still keeps her son Paulo's clothes neatly folded in the bedroom the whole family shares.

"I lost my son, I lost my son," she sobs. "All I know is the police were involved. They say there was a shootout, but where was the exchange of fire? The bullets were all going in one direction."

The four young men died in September, and their families still haven't received forensic reports.

But at the funerals friends and relatives say they started to receive anonymous messages on their cell phones with gruesome photos of the crime scene and also of cadavers riddled with holes.

Luan's brother, Alan da Silva, says he thinks these were messages from the police.

"The police were the only ones in a position to take those pictures," he says. "They wanted to intimidate us, intimidate the community and say, 'We're not fooling around.' "

The families say they believe the killings all point to torture. In the photos, CNN counted 13 bullet wounds on Luan's body, some forming a ring around his neck, and what looked like a smiley face carved into his chest.

Relatives say some of the teeth were also pulled out at the root.

"I don't know why they did it," says Luan's mother, Antonia Maria Miguel. "They were killed like animals."

But her eldest son, Alan, says police brutality is not uncommon in Brazil's poor shantytowns and suburbs.

"It doesn't matter if you're white, black, blue or gray. If you were born in poverty, you were born guilty," he says.

The Sao Paulo public defender's office agrees.

"It's a serious case itself, but it's also representative of what happens in Brazil," Public Defender Samuel Friedman tells CNN.

This month his office sent an urgent appeal to the U.N. Special Rapporteur on extrajudicial, summary or arbitrary executions to investigate the case.

Friedman says that "at the very least that the police used force illegally, but it also points that (the young men) might have been executed. It is likely they have been executed."

State officials have declined interview requests but say they are investigating.

Brazilian police killed more than 11,000 civilians from 2009 to 2013, according to a recent report by the Forum on Public Safety, a group that collects and disseminates government safety data.

The report concludes there is an "abusive use of lethal force" in Brazil.

By comparison, the reports says, police in the United States killed roughly the same number of people over 30 years -- from 1983 to 2012.

Alan da Silva says he hopes the United Nations will intervene and find out what really happened to his brother. And also step up pressure so that nothing like it happens to the baby son he left behind.