PSNI chief constable George Hamilton has insisted a probe into alleged misconduct in public office will not find any wrongdoing.
Mr Hamilton and a number of other senior officers are subject to the investigation by the Police Ombudsman following allegations about how the PSNI handled an inquiry into the awarding of a contract to supply vehicles to the force.
Mr Hamilton said he is "absolutely confident that there will not be misconduct established" and insisted he has no intention of stepping aside while the probe is ongoing.
Speaking to reporters at an Anti-Slavery Day event in Belfast, he said: "I'm confident in my ability and I have the passion to keep doing this job.
"I've got every confidence that the ombudsman will be able to get on with his job and to investigate the complaints that have been made."
Former West Yorkshire chief constable Mark Gilmore, a former PSNI officer and retired PSNI assistant chief constable Duncan McCausland were among nine people interviewed by detectives in the 2014 investigation into bribery and misconduct in public office in relation to the vehicles supply contract.
No charges were ultimately brought against any of the men - all of whom denied any wrongdoing.
Mr Hamilton, current deputy chief constable Drew Harris and current assistant chief constable Mark Hamilton are all now being investigated by Ombudsman Michael Maguire as well as a number of other less senior officers.
Dr Maguire has received complaints from a number of those investigated in the vehicle contracts probe in 2014, including Mr McCausland and Mr Gilmore.
It is understood the claims include allegations police documents were altered.
Mr Hamilton said: "We'll allow the ombudsman to do his job and we'll co-operate fully with that and let's see where the evidence takes the ombudsman because I'm confident that the outcome for us, the senior officers which have had these complaints made against them, will be a positive one."
In a statement, the PSNI said: "The chief constable, deputy chief constable and other officers completely refute the allegations made against them and are strongly of the view that these complex investigations into the complainants were conducted with professionalism and integrity.
"This position has been fully outlined in the officers' initial response to Oponi (Office of Police Ombudsman for Northern Ireland)."
The Ombudsman's Office said its investigation would be treated as a "critical incident".
"The Police Ombudsman's Office has begun an investigation into concerns about the way in which the PSNI conducted an investigation into allegations of bribery and misconduct in public office in 2014," said a spokesman.
"The office is investigating allegations of criminality and misconduct in how this investigation was undertaken by police."
The spokesman added a team of six investigators will be involved in the case.
"Given that some of the officers are above the level of Chief Superintendent, the Policing Board (the PSNI's independent oversight body) has been notified," he said.
"The office has not recommended the suspension of any of the police officers concerned."
The new ombudsman's probe, first reported by BBC NI, is expected to extend well into 2018.
Mr Hamilton was appointed chief constable in May 2014 - a month before the investigation into the vehicle contracts became public.
Mr Gilmore was suspended from his job in West Yorkshire in the wake of controversy and retired two years later having never returned to duty.
At the time of his initial suspension in June 2014, Mr Gilmore, who attended a police interview in Belfast voluntarily, insisted he had always acted with honesty and integrity.
