Several hundred Mexican troops have converged on a northern town where an arson fire at a casino killed 52 people.
Some 1,500 security forces conducted raids on nearly a dozen casinos in Monterrey, detaining three people.
Thursday, armed suspects carrying a flammable liquid burst into Casino Royale, and moments later the building was in flames. Authorities are still trying to identify some of the 52 victims.
The investigation into the attack is ongoing, but authorities are looking into whether drug cartels had threatened the casino in an extortion plot. Mexican authorities are offering a $2.4 million reward for information leading to additional arrests.
Nearly 40,000 people have died in drug-related violence in Mexico since President Felipe Calderon began a crackdown on cartels.