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.

At least three people were killed and five people were wounded in a shooting that erupted on Sunday at a restaurant in Arizona where a crowd of people was celebrating Cinco de Mayo, the police and a witness said.

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