ANKENY, Iowa (AP) — Three family members killed during a shooting last month at an eastern Iowa state park were shot, stabbed and/or strangled, according to autopsy results released Thursday.

Tyler Schmidt, 42, died from a gunshot wound and “multiple sharp force injuries,” while his wife, 42-year-old Sarah Schmidt, died from multiple sharp force injuries, the Iowa Department of Public Safety said in a news release.

Their 6-year-old daughter, Lula Schmidt, died from a gunshot wound and strangulation, officials said. All three family members’ deaths have been ruled homicides.

The Schmidts’ nine-year-old son, who was with his family on the camping trip, survived the attack without physical injuries, but investigators have not said whether he was in the tent when the attack happened.

The department confirmed Thursday that the killer was Anthony Sherwin, 23, of LaVista, Nebraska, who died from a self-inflicted gunshot wound after the family was attacked early on the morning of July 22 in their tent at the Maquoketa Caves State Park campground.

Investigators said all evidence collected substantiates that Sherwin acted alone, but police have not indicated a motive in the killings.

Police who swarmed the park about 180 miles (290 kilometres) east of Des Moines in the wake of the shooting found Sherwin’s body outside the campground but within a wooded area of the park.

READ: Police: 3 fatally shot at Iowa state park; gunman also dead