MONTERREY, Mexico Nuevo Leon state Gov. Rodrigo Medina says police have arrested five suspects in an arson attack on a casino that killed 52 people in northern Mexico.
Medina tells the Televisa network that police are looking for two other suspects.
He says that police are investigating whether the attack in the city of Monterrey was in retaliation for not paying extortion money.
The governor said Monday that authorities have not yet determined what group is behind the attack.
Thursday's arson attack on the Casino Royale saw gunmen spread gasoline and ignited a fire that trapped and killed 52 gamblers and employees.
It was the second time in three months that the Casino Royale had been targeted. Gunmen struck it and three other casinos on May 25, spraying the building with bullets, but no one was reported injured in that attack.
President Felipe Calderon is offering a $2.4 million reward for information leading to the capture of the casino's attackers, the same amount offered for the arrest of top drug lords.
On Sunday hundreds of people demonstrated outside the state government offices in Monterrey, demanding that the Medina, and the mayor of Monterrey, Fernando Larrazabal, quit.
Protesters sang the Mexican national anthem and read the names of the victims of the casino fire. Shoes - representing the victims of Mexico's ongoing violence - were lined up on the steps leading to the mayor's office.
Demonstrators say they are tired of the violence that afflicts the metropolis of 4 million as the Gulf drug cartel and the rival Zetas battle over turf.
One protester, Jose Luis Gaytan, a retiree, said he attended the gathering to remind people to stay politically active. "We must do something," he said. "We can't live isolated, misanthropic lives. We have to confront these circumstances since these people, these liars, false governments and hypocrites don't want to do anything."
Police said on Sunday that they had deployed 1,500 officers and sent Black Hawk helicopters, while the Mexican army said it was also sending 1,500 soldiers.
The government claims more than 35,000 lives have been lost since President Calderon launched an offensive against drug cartels in late 2006. Others put the total death toll nearer 40,000.