SAO PAULO (AP) ― Brazilian authorities have detained 19 people for their alleged involvement in fan violence that marked the final round of the Brazilian league this month, with some of them likely to be charged with attempted murder.

Police in three states had arrest warrants for nearly 30 people in a joint operation being called “Red Card,” with detentions made throughout the day on Thursday.

Authorities used television images and photographs to identify the fans, among them a former council member in the southern city of Curitiba and at least one of the four men hospitalized after the brawl.

Three men had been arrested the day of the Dec. 8 fight, which interrupted the match between Atletico Paranaense and Vasco da Gama for more than an hour. One of the injured men had to be airlifted from the field to a hospital.

Hundreds of fans from Vasco da Gama and Atletico Paranaense charged at each other in the stands, throwing punches and kicks and using sticks and metal bars in the fighting.

Images of the violence were sent around the world, raising doubts about Brazil‘s preparedness to host the World Cup next year.

“We hope this becomes a lesson to fans so they understand that the law still exists inside a stadium during sporting events,” police inspector Luis Felipe Fuentes told Globo TV. “A murder attempt inside a stadium is the same as a murder attempt outside the stadium.”

Authorities told a news conference in Rio de Janeiro that 12 fans had not yet been arrested by the end of the day on Thursday and were considered fugitives.

Sixteen detentions were made in Parana, two in Santa Catarina and one in Rio de Janeiro state.

Police had search and seizure warrants for the headquarters of fan groups from both teams in Rio de Janeiro and Curitiba. Officials said they seized documents and computers from an Atletico Paranaense fan group, and one of the computers contained images of past fights involving its members.

Fan groups are usually at the root of stadium violence in Brazil, with many fights pre-arranged on the Internet. Government officials, including Brazilian President Dilma Rousseff, have been calling for more strict punishment for those caught in fan fights inside stadiums.

The match was played in Joinville instead of Atletico’s base in Curitiba because the club had already been punished because of fan violence.

Last week, Brazil’s sports tribunal said Atletico Paranaense will have to play 12 matches away from home next year because of the incident in Joinville. The tribunal also said Vasco will have play eight ‘home’ matches away. Both clubs will have to play half of the games in empty stadiums. Atletico Paranaense was also fined about $50,000 and Vasco nearly $35,000.

This week, Japanese automaker Nissan dropped its sponsorship of Vasco because of the fighting, saying the violence was “incompatible with the values and principles supported and defended by the company across the world.” The planned four-year sponsorship deal had been signed in July.

A four-time Brazilian champion, Vasco lost the game 5-1 and was relegated to the second division for the second time in five years. Atletico Paranaense finished third in the 20-team standings.