The actions of the Los Zetas drug cartel at the Casino Royale in Monterrey, the capital of the northern Mexican state of Nuevo Leon, were the reason that 52 people died in a fire at the gaming establishment and not lack of safety systems at the business, Nuevo Leon Attorney General Adrian de la Garza said.

"The determining cause (of the deaths) was the actions of 18 subjects. Their armed presence and intimidation contributed to the chaos," De la Garza said during the presentation Tuesday of the results of the investigation into the attack on the casino.

A Zetas cartel crew sprayed 200 liters (nearly 53 gallons) of gasoline around the casino in broad daylight on Aug. 25, starting a fire that spread in 40 seconds and killed 52 people.

A total of 36 people, including 18 who had a direct role, participated in the attack, which was staged because the casino's owners refused to pay up in an extortion racket, the AG's office determined.

Authorities are still looking for 18 suspects, including the cartel's two top bosses in Monterrey and Heriberto Lazcano Lazcano, known as "El Lazca" and considered the top Zetas leader.

Lazcano, who deserted from the Mexican army in 1999 and formed Los Zetas with three other soldiers, is considered the intellectual author of the attacks and has a bounty of 30 million pesos (about $2.2 million) on his head.

The casino's owners will not face criminal charges, but they could be charged with administrative, civil or labor law violations, the head of the Siedo organized crime unit of the federal Attorney General's Office, Cuitlahuac Salinas, said.

The casino had eight exits - two underground, two on the roof and the rest leading into the streets - and had 40 fire extinguishers, fire retardant materials and marked escape routes, De la Garza said.

Only one exit, which was used by employees, was locked, the AG said.

"Although the casino had all the safety measures in place, they would not have been sufficient for an attack of this magnitude," De la Garza said.

Monterrey, Mexico's most important industrial city, and its suburbs have been battered by a wave of drug-related violence since March 2010, when three rival cartels reportedly went to war with Los Zetas.

Los Zetas has been battling an alliance of the Gulf, Sinaloa and La Familia drug cartels, known as the Nueva Federacion, for control of the Monterrey metropolitan area and smuggling routes into the United States.

After several years on the payroll of the Gulf cartel, Los Zetas, considered Mexico's most violent criminal organization, went into the drug business on their own account and now control several lucrative territories.

A total of 267 murders were registered in the industrial city in 2009, with the figure rising to 828 in 2010 and nearly 2,000 so far this year, according to official figures.