Cassie Sainsbury's fiancé has been named a "person of interest" in her case.

Cassie Sainbury’s fiancee Scott Broadbridge has been named as a “person of interest” by Colombian prosecutors, 60 Minutes will claim tonight.

The current affairs program will air an exclusive interview with Sainbury’s mother, Lisa Evans, and her sister, Khala, who claim the Adelaide woman doesn’t really understand the predicament she is in.

Rival Sunday Night will also air its exclusive interview with Sainsbury’s fiancee Scott Broadbridge, who believes Sainsbury will plead guilty to being a drug mule for an unknown international drug syndicate – despite continually protesting her innocence.

However, 60 Minutes' Scott Bartlett has suggested that Sunday Night could be in for a shock regarding its star witness.

“We have established here, had it confirmed from the prosecutor’s office, that the Colombian prosecutor now considers Scott, the fiancee, a person of interest in the investigation” Bartlett told News.com.au.

“They want to interview him - sit down and ask him some questions" he said. "Over here, from what I can gather, the prosecutor’s office has to rely on Scott volunteering to sit down."

Bartlett claims there's a "very big question mark" over what Broadbridge does and doesn't know regarding Cassie's case.

60 Minutes will also claim that Sainsbury had not spoken to her mother, Lisa Evans, for up to five months before her arrest, and that her family has some suspicions regarding Broadbridge.

Why are we so obsessed with Cassie Sainsbury's story? Post continues...

“It is clear there is deep feeling there. I know that Lisa hasn’t spoken to him (Broadbridge) since she (Sainsbury) was arrested. I would have thought that is very strange," Bartlett told News.com.au.

“The argy bargy…comes back to a family feud thing.”

Both 60 Minutes and Sunday Night will air their exclusive interviews at 8.30pm tonight.