When interviewed by current affairs show 20/20, Keith said he knew it was his wife from the first moment he heard her voice on the other end of the phone.
“It was my wife screaming in the background, yelling my name.”
He added that he remembered thinking, “I already know it’s her. I can tell her voice.”
“I get the phone and, [said], ‘Oh my God, honey.’ And of course she’s screaming.”
“It’s very emotional. And, ‘I love you, I love you, I love you, Oh my God, you’re here. You’re back. Where are you?’ And then the phone gets taken away from her. Like, super quick.”
More than that, he said hearing her voice ignited a wave of different emotions.
“I’m panicked but I’m happy because at this point this is the first time I’ve heard her voice,” he added. “I know she’s alive.”
The case of Sherri's disappearance has been one that has been shrouded in both mystery and speculation since she was found on November 24.
The 34-year-old was thought to have disappeared while out for a jog on November 2 and was not seen again for 22 days.
Since she was found, Keith has revealed she weighed only 39kg when she was picked up off the roadside, with her formerly long blonde hair cut short.
He has also said Sherri had been thrown from a vehicle with a chain around her waist – which was also attached to her wrists – and a bag over her head.
However, the disconnect between some of the clues has police publicly baffled, arguing they believe at least one the clues may have been planted as a "red herring".
Days after Sherri disappeared, her iPhone and headphones were found on the Mountain Goat jogging trail by husband Keith just a few kilometres from the Papinis home in Redding, California.
He had used the “Find my iPhone” app to uncover her belongings, which were found with several of her long blonde hairs tangled in the cords.
However, police believe the headphones appeared as if they had been "neatly placed" on the jogging trail.
Additionally, after Keith gave an exclusive interview to America's ABC News without police consent and released a detailed statement to Good Morning America, local authorities were forced to concur with many of Keith's disturbing claims and reports about Sherri's condition.
Sherri has since reportedly claimed her captors were two Hispanic women armed with a handgun.
The full ABC 20/20 interview is set to air in the USA today.