Walter Ackerson was only 16 years old when he disappeared. It was 1990, and the Puyallup boy wasn’t a big fan of high school. So his mom, Karen Hull, agreed to send Walter to a Job Corps facility on the Oregon coast where he could study trades like cooking and welding. Two weeks later he went missing.Now, 20 years after he disappeared, Hull knows what happened to her son: he was beaten up and thrown off a bridge.The shocking news came after a confession from Walter’s murderer, a fellow Job Corps student named Troy Culver. Culver, now 40, admitted to the killing as part of a drug treatment program that requires participants to own up to past wrongs.Karen Hull waited two decades to find out the grisly truth about her son’s final moments.At the time of Walter’s disappearance, Culver and two other Job Corps students lied and said they had no idea where he was. The four had skipped camp, hitchhiked to a beach and gotten drunk. Walter must have run away, they said.Hull never bought it. Motherly intuition told her that her boy wasn’t the type to strike out on his own. She grew frustrated with the camp when it waited weeks to tell her her son was missing. And with police when they refused to follow up on a tip that Walter had been thrown off a bridge.Then came Culver’s confession. He told police that he had gotten mad at Walter for whining about some girls. He’d punched him, over and over again, then hit his head against a tree.When he realized Walter was unconscious, maybe even dead, Culver freaked out. He enlisted the help of the two other boys to drag Walter to Newport’s Yaquina Bay Bridge. There they dropped his lifeless body 100 feet into the Pacific Ocean.Culver’s taped confession was played for the two other boys, now men. Both admitted to police their role in Walter’s disappearance. But only after cutting deals with the prosecution that will mean they’ll never serve jail time for their crimes.”It’s not justice,” Hull told the AP.