Police are analysing evidence found at the Aitutaki branch of the Cook Islands Bank which was robbed last week.
Extra police officers were sent from Rarotonga last week after intial reports that the bank had been robbed of thousands of US dollars.
Detective Inspector Areumu Ingaua says they still want members of the public to come forward with any information they may have.
He says they are trying to determine whether the crime was committed by one or more thieves.
"Our reconstruction of the case itself we believe that the person responsible may have had prior knowledge of the layout of the bank. And we also believe because of the large amount of money stolen that the offenders may be talking about it with friends and associates, and spending more than usual."
Detective Inspector Areumu Ingaua says police won't confirm or disclose how much money was stolen.