A gunman went on a deadly 30-minute rampage in Montenegro on New Year’s Day, killing 12 people in the small Balkan nation, including two children and the gunman’s sister, authorities said.

The gunman, identified as Aleksandar Aco Martinovic, 45, died of a self-inflicted gunshot wound after an intensive manhunt, Reuters reports.

According to RTCG, the country’s national broadcaster, the massacre, considered one of Montenegro’s deadliest mass shootings, began in a tavern in the town of Cetinje in southern Montenegro.

Martinovic had been “consuming alcoholic beverages all day long” when he got into an argument with someone in the restaurant, acting police administration director Lazar Scepanovic said, Reuters reported.

He went home and got a gun before returning to kill four people in the restaurant and then going to the other locations, Scepanovic said, according to the BBC.

He expanded his rampage and drove to five more locations where he shot eight more people, including the two children, prosecutor Andrijana Nastic said, RTCG reports.

“All the victims were his godparents, friends… the motive is still unknown,” Scepanovic said, Reuters reports.

According to RTCG, one of the victims was his sister Zorica Vuletić.

According to RTCG, the children he killed were brothers aged 14 and 9.

The rampage lasted 30 minutes, Scepanovic said, RTCG reports. Police were initially sent to the wrong location, he said, according to the outlet.

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“The location was indicated in the town of Bajice, where the police were sent at 5:31 p.m. and they determined that it was not the location of the incident,” he said. “On this occasion police were sent to the wrong location.”

Police located Martinovic near his home, where he shot himself in the head, Scepanovic said, RTCG reports.

“When he saw that he was in a hopeless situation, he attempted suicide,” he said. He died on the way to the hospital.

The shooter was no stranger to law enforcement and had a history of illegal gun ownership, police said, RTCG reports.

Montenegro will observe three days of national mourning starting Thursday.

Prime Minister Milojko Spajic said the massacre had “covered our country in black,” the BBC reports.

The shooting prompted Spajic to call for a review of the country’s gun ownership laws.

According to the BBC, he said the country’s Security Council would hold an emergency meeting on Thursday, January 2, to “urgently consider all options” to protect the public, including a complete ban on gun ownership.