The Attorney-General hired New Zealand prosecutor, Nigel Hampton QC, to work on the case against Fuiavailili Egon Keil.
RNZ reports the prosecutor successfully sought leave for the court to withdraw charges, saying he had reviewed the charges and found none of the allegations had been properly investigated by objective and independent investigators.
Therefore he said the whole of the investigation, arrest and prosecution case was and is deeply and irremediably compromised.
Attorney General, Lemalu Herman Retzlaff, said Mr Hampton was brought in to handle the case independently.
"He was sent the full file from the NPO, [National Prosecution Office] office, just to make sure that the Attorney-General's office was not privy to any evidence because we wanted the final decision to be fully independent," Lemalu said.
"Obviously he [Mr Hamption] is a man with extremely high experience, including being Chief Justice of Tonga, so his independent decision is one that I don't have any issues or queries with."