DES MOINES, Iowa (WHO) — A Nebraska man had been camping in a tent Friday morning about 75 yards from the Cedar Falls family he later attacked Friday morning at the Maquoketa Caves State Park, Iowa Division of Criminal Investigation Assistant Director Mitch Mortvedt stated Monday.

Around 6:30 a.m. Friday, the killer approached the Schmidt family’s tent–with the family sleeping inside–and started shooting.

But why he attacked the family remains unknown, Mortvedt said.

Sarah and Tyler Schmidt, both 42, died in the attack. So did Lula, 6. The only survivor was Arlo, 9. The killer fled to nearby woods and died of a self-inflicted gunshot wound, investigators believe.

Mortvedt said that the DCI is awaiting autopsy results, which could get released Tuesday or Wednesday.

The killer’s parents camped next to him in a separate tent, Mortvedt said. He said that the parents have been cooperating with authorities in the investigation but said that they were unaware of any previous interaction that their son had with the Schmidt family.

In fact, no witnesses told authorities that they recalled the killer interacting with any of the Schmidts during the camping trip. “There was nothing that we can that we can establish that precipitated anything other than just the random proximity.”

The killer’s mother told the Omaha World-Herald that she woke up to the sound of gunshots and screaming Friday morning and that a boy ran up to her to say that someone had just killed his family.

Mortvedt declined to say whether Arlo witnessed the attack on his family or say how he escaped. “It’s tough,” Mortvedt said about the shootings. “So heartbreaking on every level.”

A GoFundMe account has been established to care for Arlo and assist with future educational needs.