First of all - there is still no real conclusion to the quadruple homicide when Dustin was a kid. DNA proved that it was Rusty. Some believe that it was a murder -suicide by Dustin's uncle, but it could have been Dustin who discovered the bodies and said he picked up the murder weapon - then walked out of the house in a dissociated state.
When Aaron goes missing Dustin goes to Chicago to confront Rusty, who he believes is harboring the runaway teen. While confronting him, Dustin pulls out a pistol and kills Rusty.
Aquil was the "serial killer" in question and even went after Aaron in the end.
The book ends with Dustin's older son being summoned to Dustin's hometown to identify his body that was found in a drainage ditch.
It was all just - weird.
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