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 at the Casino Royale in Monterrey is one of the deadliest attacks on an entertainment center in Mexico since President Felipe Calderon launched an offensive against drug cartels in late 2006.
