The chief investigator in the southern Brazilian city of Santa Maria has said that cheap fireworks meant for outdoor use caused a deadly nightclub fire.
The death toll in Sunday's blaze reached 235 people after a 21-year-old man died of his injuries in hospital.
Police chief Marcelo Arigony said the band had chosen not to buy more expensive indoor flares.
Earlier, a court froze the assets of the owners of the Kiss nightclub.
Four people have been arrested in connection with the blaze, Brazil's deadliest in five decades.
One of those detained is the co-owner of the nightclub.
A member of the band Gurizada Fandangueira, blamed by Mr Arigony for the start of the flames, has also been arrested.
"The pyrotechnics were part of their show. The guys even wore gloves on stage so they wouldn't burn their hands," the policeman – who lost a cousin in the fire – told reporters.
He added that the band chose a $1.25 (£0.80) outdoor flare at a local shop over the $35 (£22) indoor variety.
Authorities say that more than 120 people are being treated in hospitals, and around 70 are said to be in critical condition.
Brazil is marking three days of national mourning, while politicians discuss what measures can be taken to prevent such a tragedy happening again.
President Dilma Rousseff, who had an emotional meeting with bereaved relatives, called for a stricter stance on safety rules across the country.
The fire has also prompted widespread domestic concern about Brazil's ability to host major sporting tournaments in the next four years.
The 2014 World Cup is set to be hosted in 12 Brazilian cities, while the 2016 Olympics are to take place in Rio de Janeiro.
The disaster led Congress to set up a working group on Tuesday.
It aims to write up a new federal bill in an attempt to strengthen safety regulations ahead of the World Cup.