The Independent Police Complaints Commission (IPCC) is to investigate after graphic pictures of a decapitated motorcyclist were shown to journalists.
The force has apologised for 'distress' caused
North Wales Chief Constable Richard Brunstrom used the photos of Mark Gibney, 40, to show the consequences of speeding at a private media briefing.
The force made a further apology "with sincere regret" after an earlier one was rejected by Mr Gibney's family.
His relatives on Merseyside also said they were seeking legal advice.
North Wales Police Authority has now called in the watchdog to investigate.
Councillor Ian Roberts, who chairs the police authority, said they had decided to voluntarily refer the matter "to the Independent Police Complaints Commission as they are the appropriate body to consider all aspects of this case."
Images of motorcyclist Mr Gibney, from Merseyside, were shown at a private road safety media briefing last Thursday without his family's permission.
They included one of his decapitated head, with his eyes open, inside his motorcycle helmet.
Mr Gibney was killed when his bike crashed on a bend on the B5105 between Cerrigydrudion and Ruthin in Denbighshire in 2003.
The motorcyclist was not named during Mr Brunstrom's presentation to journalists but details of his distinctive T-shirt, which bore an anti-police message, were given during the inquest into his death and the rider was identified from that.
Mr Gibney's father William, 64, said he had managed to conceal from other members of the family the horrific nature of his son's death.
"I've kept it quiet for four years. I've kept it inside me. The whole family did not know about it. All of a sudden they get to know about it this way.
Mr Gibney said he had kept facts of his son's death from his family
"The man should be just...sacked," he added, referring to the chief constable.
He said he could "never forgive" Mr Brunstrom and called for him to "be sacked".
On Sunday, in a statement, the North Wales force admitted it has made a mistake believing that the pictures shown to journalists would remain confidential.
It also issued a hand-delivered letter of apology to Mr Gibney "for the distress caused by the publicity".
But the motorcyclist's family said the apology was "not good enough" and have called for Mr Brunstrom to be sacked.
Mr Gibney's brother Paul said: "[The apology] is closing the stable door after the horse has bolted.
"Whether the meeting was private or not makes no difference because it was immoral to show such photographs of my brother."
Later on Monday North Wales deputy chief constable Clive Wolfendale issued a further apology.
Mr Wolfendale said:"The chief constable and North Wales Police apologise to the Gibney family unreservedly, wholeheartedly and with sincere regret for the distress brought to them over the past few days.
"People may make their own judgements about how and why the issue came into the public domain.
"But there is no doubt that this would not have happened had the decision not been taken to use the photographs.
Mr Brunstrom said the images were shown in confidence
"Accordingly, we extend our deepest sympathies to the Gibney family both for their loss and this most unwelcome addition to their grief and for any actions by which the family believe we have let them down we are sorry," the deputy chief constable added.
Malcolm King, a member of the North Wales Police Authority, has also apologised to Mr Gibney's family but defended Mr Brunstrom's record saying the chief constable was "extremely committed" to making roads safer.
Mr Brunstrom has been criticised by MPs and his former deputy for using the images.
He has claimed the pictures had been shown in confidence and accused some sections of the media of "distorting" the meeting.
Writing on his weblog, Mr Brunstrom said those attending the anti-speeding briefing had been warned in writing they would be "briefly exposed to harrowing images".
The invitations to the media had said the images "were not, are not and will not be released into the public domain - a point emphasised verbally during the meeting," he wrote.
"They were included as a minor part of the presentation to counter the continuing tendency in some sections of our society to trivialise road death."