I believe he was arrested in Mississippi, after a roommate became alarmed at the type & amount of child porn on the perp's computer.
He is 23, brunette, appears very overweight.
"She was so clutzy," Thompson tells ABC News Chief Law and Justice Correspondent Chris Cuomo, co-anchor of "20/20," in an exclusive interview airing tonight on "Nightline."
"I mean, she could not walk and chew bubble gum at the same time," Thompson said. "But she loved to dance. She wanted to be a ballerina."
The emotional interview took place just days before police named a former neighbor of the Thompsons as a person of interest in the girl's death on Thursday. Jarred Harrell, 24, was arrested on 29 unrelated charges of possession of child pornography.
"We are also naming Harrell a person of interest in connection with the abduction and murder of Somer Thompson," Florida's Clay County Sheriff Rick Beseler said Thursday.
Harrell lived on the street near where Somer was last seen Oct. 19, 2009. He was under surveillance for some time, police said.
Neighbors described Harrell as antisocial and withdrawn, and said they saw Somer occasionally stop to pet a little white dog near his former home.
After his arrest Thursday, authorities searched the new home of Harrell's family, particularly a shed.