The massacre happened in Uruapan, in the western Mexican state of Michoacan, on Monday, according to the state’s attorney general’s office.

Four people walked into the amusement arcade, asked questions of some patrons and began firing with military-grade weapons, the attorney general’s office said in a statement.

At least four of the dead are minors between the ages of 12 and 17, the statement added. An 18-year-old and a 39-year-old are also among the dead.

Authorities said they had located 65 “ballistic elements” that matched a 9mm caliber weapon.

Uruapan, which is home to a quarter million people, has seen episodes of grisly violence linked to drug cartels in the past.

In 2013, the bodies of seven men who appeared to have been shot were dumped in plastic chairs near a central square in the city; messages were left pinned to some of the victims’ bodies with ice picks.
And in 2006, members of a drug cartel — La Familia Michoacana — reportedly hurled five decapitated heads of rival gang members onto a dance floor there.