A disturbing 'child abuse' theory for Sherri Papini's violent abduction has emerged.

Californian jogger Sherri Papini’s mysterious disappearance and return last year prompted several theories as to what motivated her alleged captors.

Was it because of a racist blog post she didn’t really write? The work of a serial killer who had a change of heart? Was it all an elaborate hoax?

Now, a disturbing theory has reemerged that could explain why the mum-of-two was kidnapped – and then returned.

The theory, first put forward by a private investigator in December, has been featured in US TV show Crime Watch Daily.

According to the show, a source close to the investigation told them that those who took the petite 34-year-old may have thought she was a teenager or a much younger woman.

"It was sexual trafficking. I think they saw what appeared to be a young girl and took her for that purpose," the anonymous source said.

Listen: Another true crime story captured our attention last year. This one with a tragic outcome.

Papini was found branded, beaten and starved on a roadside 22 days after her disappearance from a trail near her home in Redding, northern California on November 2, 2016.

The source said the "message" Papini was branded with supports the theory as it is a practice common in child sex trafficking circles and street gangs.

A private investigator and veteran human trafficking expert also believes Ms Papini's case has the hallmarks of sex trafficking.

Bill Garcia, who was hired by Papini's family during her absence, told the US Today Show in December that her injuries were consistent with human trafficking cases.

"I suspect based on the types of injuries Sherri incurred, the beatings, the broken nose, the cut hair, especially the chains and the branding, indicate that most likely it was one of these sex trafficking groups."

According to The Today Show, Garcia was not involved with the police investigation, which has so far resulted in zero arrests.

The local sheriff, Tom Bosenko previously said investigators did not have "specific information" that the kidnapping was related to a cartel or human trafficking and has not confirmed any link since.