How accused drug trafficker Cassandra Sainsbury was caught. 

Weeks after her arrest, authorities have revealed the what led them to stop Adelaide woman Cassie Sainsbury at a Colombian airport.

The 22-year-old had cleared security, checked in her bag and was minutes away from boarding her flight home to Australia on April 12 when she was stopped by airport security.

Inside Cassie’s luggage, they discovered 5.8kg of cocaine and she was arrested.

Now, we know that was thanks to a tip-off from the US Drug Enforcement Agency, who were suspicious after her plane ticket to Colombia via London was purchased last-minute by a party in Hong Kong.

Cassie Sainsbury was arrested and detained after she was found in possession of 5.8kg of cocaine. (Image via Facebook.)

Bogota airport's narcotics chief, Commander Rodrigo Soler, told The Australian the DEA alerted Colombian authorities to their suspicions, with the plane ticket just one of several red flags.

Mr Soler said security approached Cassie after they saw the alert, which came up after she'd passed security.

"The alert said check this person so we pulled her aside and we searched her luggage and we arrested her. We asked 'is this your bag, did you pack this?'. She said 'yes'," he told the newspaper.

Cassie is in a South American jail awaiting trial, where she could be sentenced to 25 years in prison for drug trafficking.

The South Australian woman's family insist she's innocent and that she was given the drugs packed in headphones she'd purchased from a man the day before she left.

Her mother Lisa Evans said she bought the headphones from him to give as gifts to friends, family and the bridal party of her upcoming wedding.

Ms Evans said a lawyer had advised her daughter to plead guilty to avoid a potential jail sentence of between 18 and 25 years.

Nine News reports the sentence could be reduced to four years if she supplies information about the man who allegedly gave her the drugs.