Drug mules Michaella McCollum and Melissa Reid could face a six-month investigation if their guilty pleas are not accepted, the Peruvian prosecutor in charge of their case has said.
Juan Mendoza made the comments after the women, both 20, made a second appearance before a judge at Sarita Colonia del Callao jail, in Callao, near Lima. He did not give details of the private hearing but suggested the women's confessions had not yet satisfied prosecutors.
Last week McCollum, from Dungannon, Co Tyrone, and co-accused Reid, from Glasgow, pleaded guilty to drug smuggling. They had hoped the behind-closed-doors admission would be enough to secure a shorter sentence.
But prosecutors have demanded more information before accepting their admissions of guilt which the women hope will bring their jail time down to six years and eight months.
Mr Mendoza, speaking to The Associated Press, would not discuss whether the women had explained to them how they got the cocaine, or who it was from.
McCollum and Reid initially claimed they were kidnapped, held at gunpoint and forced to board a flight from Lima to Spain with 24lb of cocaine in food packets hidden inside their luggage when they were arrested.
An Irish priest has said the pair are in great health as they await to hear of their fate.
Father Maurice Foley visited the pair last Saturday where he found them sitting under a parasol in a yard in the jail drinking coffee and making phone calls.
"(They are) brilliant. Very, very well," he said.
"They weren't in a cell. They were out in a wide open space sitting at a table with a parasol, they were talking and drinking coffee.
"As well as that they had telephone communication and they could use it for calling home. I thought they were in great form actually."
Fr Foley, who had to wait a month to be allowed in to visit the young women because of a flu outbreak in the prison, said the pair can sit out all day every day and make as many calls as they wish, so long as they have money to cover it.
Fr Foley said he did not speak to the pair about their legal case. But he said that he took McCollum to one side during the visit and advised her that she should not expect to secure a sentence as low as one year. The priest said he expected a seven year sentence, which could be reduced at a later stage.
McCollum was very emotional when the priest warned her about the jail sentence. He said the women were sadder and wiser for the experience.
Fr Foley also suggested they might get moved after sentencing to a new prison in the north of Lima, which has an area dedicated for foreigners.
The priest said local media reports had not done the women any favours, with stories saying that they had "behaved badly" in Ibiza and were then sent to Peru to act as mules.
Fr Foley said the prosecutors want the girls to hand over names and addresses of the gang who coerced them into the trafficking.
"They don't have that. All they have is the name of a cockney Englishman by the name of Jake or Joe and that's no good," he said.
"I think they just don't have that information themselves. My firm belief is that they were conned, they were backed into a compromising situation and their handlers worked on that and got them to go to customs with drugs.
"What very likely happened was that people coming behind them in the queue in the airport were the ones who walked through with the drugs."