FORT SMITH, Ark. (AP) — Two people in Arkansas were found fatally stabbed and a third person was shot and killed by an officer whose neck was slashed after he found a man beating one of the stabbing victims with a rock, authorities said Sunday.

It happened around 6:20 a.m., when Fort Smith police received a 911 call about a man assaulting a person who was on the ground. The responding officer discovered Christofer Conner beating a 15-year-old boy in the face and head with a rock, said Fort Smith Police Chief Danny Baker.

Police in Fort Smith, located about 160 miles (260 kilometers) northwest of Little Rock, later determined the boy was Conner’s son.

As the officer tried to place Conner, 40, in restraints, the suspect pulled out an edged weapon and sliced the officer’s throat and neck, Baker said. The officer then fired two shots at Conner, killing him.

The officer was rushed into emergency surgery, and was in stable condition on Sunday afternoon, Baker said. His name was not immediately released.

The boy was taken to a local hospital, where he was pronounced dead. He had sustained multiple stab wounds and other injuries, Baker said.

Other officers at the scene went inside a home and discovered “evidence of an extremely violent attack,” Baker said. They found the body of 42-year-old Julia Marie Moore inside the residence. Authorities believe she had been fatally stabbed.

A 5-year-old child was found safe in the home. The child was later placed with other family members, Baker said.

Police did not immediately say what the relationship was between Conner and Moore, nor did they identify the parents of the 5-year-old found in the home.

The police department asked Arkansas State Police to lead the investigation because it involved an officer shooting.

The injured officer and a second officer were placed on paid administrative leave while the investigation continues.

Baker called Sunday’s incident an “unimaginable tragedy.”