The Garda Síochána Ombudsman Commission has opened an investigation into the circumstances of Detective Superintendent Colm Fox's death, who was the lead investigating officer in the Regency Hotel shooting.
It made the announcement following today's decision that the DPP was dropping the charges against 26-year-old Patrick Hutch who was accused of the murder of David Byrne on 5 February 2016.
Det Supt Fox was found dead at Ballymun Garda station on 10 February last year.
Foul play was not suspected and his death was treated as a personal tragedy.
In a statement today, GSOC said [it] "has moved from an examination under section 91 of the 2005 Act to an investigation into the circumstances giving rise to the death of the late Det Supt Fox".
It also appealed for cooperation from gardaí and other agencies.
It said: "The ability to conduct a proper oversight investigation of these events will be dependent on the cooperation given to GSOC by the gardaí and other agencies.
"Given the limited resources of GSOC, considerable cooperation from all parties involved will be required for an effective investigation to take place."
It added: "GSOC is conscious that behind the events which have given rise to this investigation families and friends continue to mourn the deaths loved ones."