Brazilian police have arrested the co-owner of a nightclub where 233 people were killed in a fire, according to the AFP news agency.
Police also apprehended two members of a band that was performing at the club, the report said.
Witnesses said a flare or firework lit by members of the band onstage had started the fire, which broke out early on Sunday morning.
The fast-spreading blaze raged through the crowded Kiss nightclub in Santa Maria, with a cloud of toxic smoke setting off panic as party-goers gasping for air rushed to the exit.
Security guards tried to block people from leaving the club, survivors and rescuers have said.
Brazilian bars routinely make patrons pay their entire tab at the end of the night before they are allowed to leave.
"It was chaotic and it doesn't seem to have been done in bad faith because several security guards also died," police inspector Marcelo Arigony said.
A preliminary investigation also found that the club's exit was blocked by the bodies of those already dead.
Police have said an arrest warrant has been issued for another owner of the club.
Firefighters stand outside the burnt out clubThe detentions were for investigative purposes, and a police official said they were "temporary", according to AFP.
Many of the 233 victims were under 20-years-old. Around 117 others were injured.
Funerals for some of the victims were being held on Monday in Santa Maria, a university city in the south of the country.
The blaze broke out while the band, called Gurizada Fandangueira, was performing in the club, which was overcrowded with some 1,500 people.
Television images showed black smoke billowing out of the nightclub as shirtless young men who had attended a university party joined firefighters using axes and sledgehammers to pound at windows and pink exterior walls to free those trapped inside.
Bodies of the dead and injured were strewn in the street and panicked screams filled the air as medics tried to help.
Hours later, the bodies of the victims were lined up in a community gym, as desperate family members identified their relatives.
Survivor Michele Pereira told the Folha de S Paulo newspaper she was near the stage when members of the band lit flares that started the fire.
"The band that was onstage began to use flares and, suddenly, they stopped the show and pointed them upward," she said.
"At that point, the ceiling caught fire. It was really weak, but in a matter of seconds it spread."
One member of the band was killed while five made it out safely.
Brazilian President Dilma Rousseff flew back from a summit in Santiago, Chile, and declared a national three-day mourning period for the victims.
"We are going to make it through this tragedy," Ms Rousseff said.
An event scheduled for Monday to mark 500 days to go until the 2014 World Cup in Brazil was scrapped out of respect for the victims.