A man and woman were fatally shot outside an Oklahoma Walmart on Monday by a man who then killed himself.

The victims were gunned down in a car in the parking lot just before 10 a.m., Duncan Police Chief Danny Ford said.

The shooter’s body was found outside the vehicle.

The three, who were not publicly identified, knew each other, Ford said, but he declined to describe the relationship.

Authorities provided no motive, but people who identified themselves as relatives of the victims told KOKH-TV in Oklahoma City that the shooting stemmed from a domestic dispute between a husband and wife.

All three people were dead by the time police arrived, just minutes after the shooting, and a semiautomatic handgun was recovered, Ford said.

A Walmart spokesperson said no staffers were injured and the store wasn’t evacuated.

Nearby schools in the town of 25,000 about 80 miles south of Oklahoma City were placed on lockdown as authorities investigated, the Duncan Banner reported.

The shooting was at least the third at a Walmart this year.

A 21-year-old man allegedly targeting Mexicans gunned down 22 people at a Walmart in El Paso, Texas, on Aug. 3, in one of the deadliest mass shootings in US history. Four days earlier, a man police said was a disgruntled Walmart worker killed two employees at one of the stores in Mississippi.

Additional reporting by Tamar Lapin, with Wires