The last-minute purchase of a plane ticket in Hong Kong for the Adelaide woman to travel to Colombia via London was a red flag that raised the suspicions of US drug authorities, who alerted their Colombian counterparts, The Australian reported.

The plane ticket was bought by an unknown party for Ms Sainsbury, a former personal trainer, to travel to the South American country alone, and for a relatively short period.

Ms Sainsbury, 22, arrived in Colombia on April 3, and Channel Seven reported that US authorities might have forwarded her passport details to Colombian police as early as April 5, warning she might try to smuggle drugs.

Police arrested her inside El Dorado International Airport, in Colombia's capital Bogota, on April 11 as she prepared to board a flight to London.

Reports suggest Ms Sainsbury had checked in her suitcase and was about to clear the final immigration check when she was stopped.

Colombian police allege that, when they searched her suitcase, they found 5.8 kilograms of cocaine concealed in 18 headphone boxes.

She was handcuffed and photographed in front of the drugs, before being taken to El Buen Pastor women's prison in Bogota, where she continues to be held.

Colonel Rodrigo Soler, the airport's head of narcotics, told The Australian that Ms Sainsbury's travel profile fitted a well-established pattern of drug mules, which raised the suspicions of US authorities.

Ms Sainsbury's family claims she had bought the headphones as gifts for friends and members of her bridal party, ahead of her wedding to her fiance, Scott Broadbridge, in February next year.

Her sister, Khala, said that, in the days before her flight home, her sister "was with somebody she had met that could speak English and she was sightseeing".

"He was showing her around," Khala said of the local man.

When Ms Sainsbury saw some headphones she was going to buy for gifts, the man told her he knew someone who could get them more cheaply, Khala claimed.

"She did that and got them handed to her [on the] Wednesday morning before she left. She just put them straight into her suitcase," Khala said.

Colombian police released this photo of Cassandra Sainsbury with the alleged drugs. Photo: AP

Her family claims she had no idea the drugs were concealed in the headphones, and say she is now facing up to 25 years in jail for a crime "she did not commit".

On Tuesday, Lieutenant Colonel Jorge Triana told Colombia's W Radio station that Ms Sainsbury's claim that she was deceived was probably untrue, and in any case it did not excuse her actions.

"Everyone who is caught says exactly the same thing," he said. He claimed many foreigners were lured by promises of fast fortunes. "But they know what they're doing," he said.

Meantime, a fundraising page Ms Sainsbury's family set up to help pay for her legal costs has been shut down after raising just over a quarter of its target.

Khala had set up the FundRazr page with the aim of raising $15,000, but the page was soon flooded with negative comments by people who doubted her story and questioned why they should contribute.

The account has since been closed after receiving just $4232 in donations from 105 people - well short of the $15,000 the family hoped to collect to help cover legal bills.

After initially speaking out about Ms Sainsbury's case, her family are now keeping quiet on legal advice.

Ms Sainsbury and Mr Broadbridge's Facebook pages have also been closed.

Jay Williams, a Sydney barrister who is providing legal advice to Ms Sainsbury's family, declined to comment when contacted by Fairfax Media.