A 19-year-old killed his mother and two neighbors before turning his gun on himself in a shooting that brought SWAT and various emergency vehicles to a rural area in Texas, authorities said Sunday.

Uvalde County Sheriff Charlie Mendeke said Dylan Westerburg gunned down his mother Friday afternoon in their home near Uvalde, about 85 miles west of San Antonio. He then went next door and killed two brothers, Arthur and Phinny Norton, Mendeke said.

Mendeke said investigators haven't determined a clear motive for the shootings. Westerburg lived with his mother in a small cabin about 20 yards from the Nortons' mobile home on the brothers' property.

Phinny Norton, 60, had some "sort of romantic relationship" with Westerburg's mother, 42-year-old Jennifer Diane Jacques, Mendeke said. Deputies had been called out to the property in the past because of domestic disputes but "nothing violent," Mendeke said.

Authorities arrived at the scene after a teenage witness called them. The teenage boy was with Arthur Norton, 58, when they saw shotgun shells and broken glass as they approached the Nortons' mobile home, Mendeke said.

"Mr. Norton enters the house," Mendeke said. "The kid who was with him hears and sees a gun blast and sees Mr. Norton fall to the floor" before running to call authorities.

When officers arrived they heard another gunshot. Not knowing whether there were multiple gunmen or whether the gunman was dead, authorities surrounded the homes and began evacuating people nearby.

It was during that search that they found Jacques' body. The family's dog had also been killed.

Mendeke said he called in about 50 to 60 officers from different agencies as well as a Texas Department of Public Safety SWAT team out of caution. Authorities closed the road leading to the property and they stayed there overnight.

"I didn't know how many shooters I had in the Norton residence when I found the mother," he said. "You're looking at farm- and ranchland. You could get into a dangerous situation."

The SWAT team finally entered the Nortons' mobile home on Saturday afternoon and found the Norton brothers and Westerburg dead inside. Mendeke said Westerburg had shot himself in the head.