The letter was sent to the Prime Minister and copies surfaced in the media.
The Assistant Commissioner of Police, Le’aupepe Fatu Pula, says the un-signed letter claims that there are questionable practices within the Ministry of Police, especially at Tafaigata Prison.
There are also allegations of conflicts of interest and immoral behaviour among senior police officers.
Le’aupepe says the investigation is expected to be completed by next week.
An officer from the Ombudsman’s office is working with Police officers from the Professional Standards Unit on the investigation.
Leaupepe said that the investigation covers all the allegations raised in the anonymous letter and the truth will come out once the investigations are completed and the report will be referred to the Police Commissioner.
He is also encouraging the author of the letter to come forward if he or she wants to.
Meanwhile, a Samoan policewoman has been forced to leave a workshop on domestic violence she was attending in Fiji after police began an investigation involving her.
Leaupepe Fatu Pula, says the officer returned home on Tuesday, one day after the workshop started.
The officer is attached to the Ministry of Police and Prisons’ domestic violence division and she had undergone training in the United Kingdom.