Stephen Silver, with an address in Foxford, Co Mayo, had pleaded not guilty to the murder of Detective Garda Colm Horkan, who was shot dead in June 2020.
Detective Colm Horkan died after being shot eleven times with his own standard issue firearm just off Main Street in Castlerea, Co Roscommon on June 17 2020.
His gun's entire magazine was emptied. Fifteen spent cartridges were found at the scene.
At the outset of his trial, Stephen Silver pleaded guilty to manslaughter by diminished responsibility, but denied the murder charge.
One of the main issues for the jury to decide related to his mental state at the time.
A forensic psychiatrist called on behalf of the defence concluded that he was suffering a relapse of bipolar affective disorder when he shot Detective Horkan.
The expert called by the prosecution disagreed.
The jury was sent out on Tuesday to consider the evidence. This morning, they were told they could return a majority verdict, but less than two hours later, they told the judge they couldn’t reach agreement.
A date for his retrial will be set next month.
