Desiree Young and Kaine Horman sat down for an interview with Priya David Clemens of CBS Portland, Ore. Affiliate KOIN-TV.
They also say Terri Horman failed two polygraph tests.
And Young says she suspected Terri from the start.
Terri is the last person known to have seen the second-grader alive, in his Portland area elementary school, on June 4. She hasn't officially been named a suspect or person of interest by investigators, but has apparently been the focus of their probe.
Kaine has filed for divorce from Terri, moved out of the home they shared, taking their young daughter with him, and obtained a restraining order against her - all after police told him of aagainst him hatched by Terri.
As Young and Kaine began the interview, information had just come to light about the restraining order.
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In it, he says flat-out that Terri had something to do with Kyron vanishing.
"Because she's not telling the truth," Kaine replied.
"It all just adds up to (her lying)," Young agreed.
Both say they passed polygraph tests early in the probe, but they claim Terri didn't, even when police gave her a second chance.
"She went in," says Kaine, "and went through part of it and walked out in the middle of it, and then delayed for well over a week before the second one. For her to wait that long and fail is a huge concern."
Young says she doesn't think it's possible she and Kaine could be wrong about the suspicions they harbor. "You don't fail a polygraph twice if you're not guilty," she asserts. "I can tell you what I ate that day, and she can't tell you where she was."
In public, the family appeared united in their grief right after Kyron went missing, but Young now says she suspected Terri from the moment she heard Kyron was missing. "I've had feelings since I got the phone call," Young told Clemens. "I thought, 'She'd better not have done anything to my son!" '
While there's no proof Terri did anything to Kyron, Kaine spoke for the first time about the revelations his wife may have plotted to have him killed.
"In the restraining order," Clemens pointed out, "you state, 'My wife tried to hire someone to murder me.' How hard to write that?"
"It still hasn't even sunk in," Kaine responded. "I'm focused on Kyron., and my brain still cannot process the statement."
Kaine said he and Terri didn't have money or relationship problems and that neither was seeing anyone on the side, as far as he knows.
Kaine says his wife changed after the birth of their daughter, Kiara, 19 months ago. "It's extremely shocking, based on where we are today, but things have definitely changed from who she used to be. I think there was some post-partum depression involved after the birth of Kiara. (Terri was) moody, and cried a lot.
It lasted, he says, "until recently, the past few months; some of it may have been hidden from me, more than I know about."
Young and Kaine say they're holding out hope Kyron is alive, hoping someone other than Terri was involved, because that could mean Kyron is, indeed, alive.