São Paulo police said Sunday at a news conference that eight people were killed after gunmen entered a clubhouse for fans of the soccer team Corinthians, ordered people to lie face down, and then shot several of them in the head.
The armed gunmen stormed the Pavilhao 9 clubhouse, which is underneath a highway overpass, on Saturday night, while fans were having a barbecue and making signs for an upcoming game, the Associated Press reported.
The assailants ordered people to lie down and then started shooting them in the head. Seven people died from their wounds, while an eighth person was running away when he was shot and later died at the hospital, Reuters reported.
Corinthians play rivals Palmeiras in the semifinal of São Paulo state championship later on Sunday. The game is still scheduled as planned, Reuters reported.
There has been past violence between fans of the rival soccer teams, but police said the killings were not related to the game.
"Through witnesses, we are already exploring a line of investigation, which is not leading us to believe it was caused by fan rivalry," Detective Arlindo Jose Negrao was quoted as saying by the AP. "We even have possible suspects."
Police said they believed the shooting were possibly related to a dispute between drug dealers, and suggested the clubhouse had ties to gangs, according to Reuters.
The BBC's Wyre Davies reports that violence related to soccer in Brazil is a growing problem both directly and indirectly, because some people use the clubs to organize criminal activity around the stadiums.