Previously on Unsolved.

In 2009, I was heading up to another homicide conference up in Green Bay.

And on my way up to Green Bay, I get a phone call from my boss, Kemp Begansky at the time the chief.

And he says, I need you to come back. Greenfield has arrested this guy on a sexual assault case, and they uncovered information regarding the zero case.

So at first, everything was pretty standard when they searched Acker's condo.

The things that really disturbed them was when they got down to the basement,

there was a model police station and a model fire station.

And inside the walls were little pictures of dead and missing children.

And above each one, there were these little LED lights that were programmed to light up,

kind of like in a museum would be.

And these matchbox cars, and on the bottom of the matchbox cars, were the names of all these

victims from throughout the country.

And obviously, John Zero's picture and his name on a car was part of it.

Police also recovered a photo album and a journal about John's case, with entries that started in 1976 and spanned decades.

I've never seen anything like that before.

It was like, oh, man, I think we got something here that we need to look at.

And he is a pedophile.

There's no question about it.

And his age preference is that early teens, 13 to 15 years of age, that ballpark.

From the Milwaukee Journal Sentinel, this is Unsolved.

A murdered teen, a 40-year mystery.

I'm Gina Barton.

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