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EL DORADO, Kan. (AP) — Butler County Sheriff Kelly Herzet said Thursday in a news conference that he has his doubts that Adam Herrman, who disappeared from Towanda, Kan., in 1999 when he was 11-years old is still alive.

Herrman’s adoptive parents never reported him missing.

But on Thursday, Sheriff Herzet announced that the reward to help find Adam Herrman has increased to $100,000. The previous reward was already a substantial sum of $50,000, but Herzet said an anonymous donor has put forward more funds in hopes that the additional money will convince someone to come forward with information.

Adam Herrman disappeared in 1999 from the family’s Towanda home in southeast Kansas but wasn’t reported missing until 2008 when his older sister contacted authorities. He remains the subject of a missing person investigation.

His adoptive parents, Doug and Valerie Herrman, were convicted in 2011 for receiving state adoption subsidies after he went missing.

The National Center for Exploited and Missing Children says Adam had numerous scars on his abdomen, a scar on his left thigh and a birthmark on his lower back.

The age progression photo of Adam shows what he may look like at 26 years old.