The cost of the police investigation into the murder of Nairn banker Alistair Wilson has reached £1.5m, Northern Constabulary has confirmed.
Mr Wilson was killed on the doorstep of his home in Nairn
The 30-year-old father was shot dead on his doorstep by a mystery gunman in November 2004.
The inquiry is believed to be the most expensive conducted by the force.
Chief Constable Ian Latimer admitted that he was frustrated by the lack of progress in the case. Police have yet to establish a motive.
Mr Latimer told a national newspaper he remains committed to ensuring that the offender or offenders be brought to justice.
On the day of the murder, Mr Wilson's wife Veronica had answered the door of the family home to a man asking for her husband, who was preparing his sons for bed.
A few moments later Mr Wilson, a business banking manager with the Bank of Scotland, was shot at point-blank range.
The semi-automatic pistol used in the killing was found in a drain nearly a mile from the murder scene.
In January, officers travelled to Germany and the Czech Republic to trace the history of the gun and the ammunition.