A nearly four-month police investigation revealed that there were few signs that a Kennewick sixth-grader would kill his teenage sister last summer and then turn the gun on himself.

Some friends and neighbors described Ethan Austin, 12, as infatuated with guns and first-person shooter video games, according to police reports recently released under the state Public Records Act.

But most who knew the Boy Scout say he was an outgoing child who was friendly and often played with other children in his neighborhood.

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Ethan appeared happy and normal the weekend before the June 9 shooting that left Kaitlin Austin dead, police reports said. Evidence shows the 16-year-old junior at Kamiakin High School was shot eight times and sexually assaulted.

During the weekend, Ethan had a sleepover with a friend, rode bikes through his neighborhood and watched his sister play softball the night before the shooting.

“(A close friend) stated that there didn’t appear to be any problems with Kate and Ethan at the game,” a Kennewick police detective wrote. “(The friend) described them as acting normal and mellow with each other.”

Something changed by Monday, the day of the shooting, as friends reported that the usually social Ethan was different at Desert Hills Middle School. It appeared he was withdrawn and troubled by something.

However, Ethan — who reportedly got angry easily and had Attention Deficit Hyperactivity Disorder (ADHD) — did not mention to friends that he was upset or depressed, police reports said.

“(A classmate) stated that on Monday he could see in Ethan’s eyes that something was really bothering him,” a Kennewick police detective wrote. “(The friend) stated Ethan was either really tired or something happened.”

An adult neighbor even noticed something was different with Ethan as he walked from the bus stop to his Hansen Park home after school, police reports said. The smile he usually flashed was gone and it seemed like something was wrong.

The woman told police Ethan partially waved at her and his “visible outward mood was so different.”

Not long after Ethan came home, he got a 9mm pistol from a case in his parents’ room and shot Kaitlin, who had arrived home shortly before. Evidence suggested shots were fired from a hallway and inside Kaitlin’s bedroom.

The Kamiakin softball star was getting ready to celebrate an anniversary with her longtime boyfriend, who was leaving for college soon.

Ethan had trained with the gun for competitions, and it was usually stored unlocked in the house, said the reports.

Kennewick attorney Scott Johnson, who represents the Austin family, had previously said he thought the gun was locked up the day of the shooting.

The bodies were found by their father, Andrew Austin, on Kaitlin’s bedroom floor, police reports said. Andrew is Ethan’s biological father and had raised Kaitlin from the time she was a baby. Ethan had only just learned they had different fathers.

Police spent the weeks following the shooting conducting dozens of interviews, scouring social media accounts and phone records, and collecting evidence to send to the Washington State Patrol Crime Lab.

Pornography websites were found on a cellphone used by Ethan, and some references to gun violence were scribbled in a Mad Libs book in his room. However, there were no indications on social media that Ethan planned to kill Kaitlin, and no suicide note was found, according to the police reports that totaled hundreds of pages.

Police investigated the possibility that someone else killed the children, though they assured the public at the time that they believed no one else was involved.

The forensic pathologist who conducted the autopsies ruled in early August that the case was a murder-suicide, but police and coroner officials waited until they received DNA test results in late September before making their conclusion official.

Nearly four months after the shooting, Benton County Coroner John Hansens and police officials ruled the death investigation a murder-suicide. Ethan was identified as the shooter in a news release issued Oct. 10.

“No motive was identified for the incident,” Hansens said in the release.

But Prosecutor Andy Miller — in an email later to Hansens and Kennewick Police Chief Ken Hohenberg — disagreed with the wording in the public statement that no motive was developed during the investigation. Miller told the officials the discovery of Ethan’s DNA directly contradicted their news release and the notion that there was no possible motive.

Johnson also told the media there was no evidence to suggest a clear motive for the shooting.

“Unfortunately, I think the end result is that the public is being misled,” Miller wrote in an email to Hansens and Hohenberg.

Police told the media they released few details about the case and the investigation out of deference to the Austin family. They said the family was clearly devastated and they wanted to balance the needs of the Austins with the release of information to the public.

The Austins are trying to move forward with their lives and honor the memories of both children, Johnson said.