The victim, Dalton Williams of Pierre, was found lying in the entryway of the accused shooter's house around 5:30 p.m. Tuesday with a gunshot wound to the chest. Paramedics rushed the high school sophomore to a nearby hospital, but he later died.
The accused shooter was arrested at the home on a first-degree murder charge and was being held Wednesday in Hughes County, Pierre Police Chief Bob Grandpre said.
The local prosecutor said the teen is being charged as an adult. He has not yet been arraigned or indicted, so The Associated Press is withholding his name because he is a minor. His attorney didn't immediately return a phone message.
The boys, both 16, were classmates at Riggs High School.
A 16-year-old witness who was hanging out with the boys told detectives that Williams and the other boy began to wrestle around jokingly after arguing about a paintball game.
The accused shooter then retrieved a semi-automatic shotgun, walked into the kitchen area and pointed it at the witness, according to the arrest affidavit.
The witness said he heard the gun click, then saw the accused shooter take a shotgun shell from a drawer, load the gun and point it at him again. The witness said he then heard another click, according to the affidavit.
The witness told police he was trying to leave the house through a sliding glass door when Williams stepped in between him and the accused shooter. The witness told detectives that the gun fired and he observed a splatter, according to the affidavit.
The witness then left the house and called 911.
Grandpre said law enforcement, Pierre School District personnel and mental health professionals are providing support to the school and community.
"We're continuing the investigation to make sure we understand everything that we believe happened inside the house," he said Wednesday.