Police in Glendale, Arizona, said three people are dead and five injured after a shooting at a restaurant Sunday night. No one has been arrested, but investigators believe multiple shooters were involved.

NBC affiliate KPNX of Phoenix reported that the restaurant El Camarón Gigante was holding a Cinco de Mayo party at the time.

The fatal shooting Sunday night at a restaurant and event venue in Glendale, Arizona, was an “isolated incident that involved individuals that were known to one another,” the city manager’s office said in an update Monday.