John Walsh, the americas most wanted guy

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So I am slightly familiar with his backround, I do know his son died and I think? that's what started him hunting down all these killers. But I googled him and didn't find too much info, just on his website it was vague about what happened to his son and the past. What happened to his son? Can anyone fill me in? Another website said maybe jeffrey dahmer had something to do with it, but I didn't see anything like that on the www.amw.com website. thanks!