Mexican authorities have arrested a police officer in connection with an attack last week on a Monterrey casino that killed 52 people, the attorney general's office said Thursday.

The Nuevo Leon state police officer is suspected of having taken part in the Aug. 25 arson attack on the upmarket Casino Royale, Jose Salinas, an official at the attorney general's office, told a televised news conference.

The attack was one of the worst killings of civilians in recent years in Mexico, where drug-related violence has claimed more than 42,000 lives since President Felipe Calderon went to war on the drug cartels after taking office at the end of 2006.

Five other suspects in the attack, whose arrests were made public on Monday, are believed to be members of the Zetas drug cartel, which has ravaged the prosperous northern city of Monterrey over the past two years.

Law enforcement agencies have been infiltrated by the cartels, who can often offer them more money than the state.

Nuevo Leon has fired much of its police force and increased pay to try and root out the corruption.