Nuevo Leon security spokesman Jorge Domene says Baltazar Saucedo Estrada is a main hitman that was sought on a 15 million-peso reward because of the casino attack.
Domene said Friday 38-year-old Saucedo was detained in Monterrey because he looked suspicious.
On Thursday, police ordered him and another man to stop their vehicle. They gave chase, and crashed into a car. Also known as "mataperros," or dog killer, Saucedo was identified hours later as he was being processed.
Authorities have arrested 17 of 32 suspects in the Aug. 25 casino arson.