The file into the killing of Det Garda Colm Horkan has been completed and runs to 10 volumes, a court was told.
Sgt Mark Mahon said the documents are with the DPP and will take time to be processed.
He told Judge James Faughnan at Harristown District Court real progress had been made in the investigation.
Stephen Silver, 44, is charged with the murder of Det Garda Horkan in Castlerea, Co Roscommon on June 17, but a sick note was handed into the court which excused him from appearing via video link.
Sgt Mahon told the judge: “The file is with the DPP. It is being practically reviewed and an officer has been appointed there.
“It will take a substantial length of time, the file consists of a total of 10 volumes.
“However, the DPP’s office is actively looking into the file at the moment and we hope to have directions as soon as possible. Things are progressing,”
It is the eighth time Silver, whose address was given as Aughaward, Foxford, Co Mayo, has been deemed unfit to take part in the proceedings at the court, which is located beside Castlerea Prison.
Defence solicitor Martina Moran told a previous sitting of the court her client was being treated at the Central Mental Hospital and that video link facilities had been arranged there.
Sgt Mahon told previous sittings of the court the investigation included more than 350 house-to-house enquiries and in excess of 200 written statements.
It included more than 250 exhibits and the contents of 10 electronic devices, while gardai also spoke to a person in Australia as part of their inquiries.
Judge Faughnan remanded Silver in custody to appear before Harristown District Court by video link on October 16 for DPP directions.
