EVERETT — When he was first asked what happened to his nephew Oct. 16, Andrew Henckel reportedly was mystified.

Dayvid Pakko, 6, had simply disappeared from his Lynnwood apartment, he said.

“I don’t have the slightest clue where he’d go or what had happened,” Henckel is quoted as telling detectives as a frantic search began for the missing boy. “… I’m just assuming he got lost or something.”

Hours later, after the first-grader’s body was found in a nearby trash bin, Henckel detailed how he drowned the child in the family’s bathtub, according to documents filed Friday in Snohomish County Superior Court.

An affidavit deputy prosecutor Matt Baldock filed along with the first-degree murder charge says Henckel told Snohomish County sheriff’s detectives that as he held the boy underwater he “just kinda let it happen.”

Henckel, of Kerrville, Texas, had been visiting his sister. He briefly was left alone with the boy. That’s when he allegedly told detectives he decided to end the child’s life.

The prosecutor excerpted the part of Henckel’s alleged statement when detectives asked him to explain his behavior. Henckel claimed he wasn’t thinking about the result of holding the boy underwater.

Detective: “Okay. But what did you know would happen?”

Henckel: “That he would drown.”

Detective: “That he would drown?”

Henckel: “Yeah.”

Detective: “Is that what you were trying to accomplish? …”

Henckel: “Yeah.”

Detective: “You were trying to drown your nephew? Why?”

Henckel: “I don’t know.”

Detective: “So you don’t know why you … drowned your nephew?”

“Wasn’t really thinking,” Henckel reportedly said. “I just kinda did it.”

Henckel allegedly spoke with detectives in a recorded interview after being advised of his legal rights. He reportedly described his attempt to cover up the death, including taking the boy’s body out to the trash bin and using towels to dry the bathroom floor.

About 200 people participated in what became a nine-hour search for the missing boy. Early on detectives were suspicious of Dayvid’s disappearance. They were told that he had autism but no history of wandering. They found pajama bottoms he reportedly was wearing turned inside out, on top of the washing machine.

Henckel has been jailed since the boy’s body was found, his bail set at $1 million. At 6-foot-4, his attorney earlier said he’s known as a “gentle giant” by his family.

After Henckel’s arrest, his father said he doesn’t believe his son is capable of murder and that the teen lives with Asperger syndrome, a form of autism.

Scott North: 425-339-3431; north@herald net.com. Twitter: @snorthnews.