Street Wize News ( Raw &Unkutt )

CNN) -- Fifteen people were killed Wednesday at a carwash in the western Mexican state of Nayarit, the state attorney general's office told CNNMexico.com.

The attack happened at a business called the Gamboa carwash in the capital, Tepic, and is presumed to be the work of a drug cartel, the state-run Notimex news agency reported, citing local police.

A man had been killed the night before in the same area, police said.

Initial reports by investigators said witnesses heard the gunfire Wednesday morning, only two blocks away from the offices of the federal police, Notimex reported. The federal police responded to the scene to find 15 people dead, including clients and employees of the carwash, the news agency said.

Investigators found hundreds of shell casings from assault rifles.

The mass slaying resulted in the closure of nearby businesses and schools.