The Police Service of Northern Ireland top officers' accusers are themselves nine senior experienced police officers, including a former chief constable of West Yorkshire police, it was confirmed on Thursday.
Chief Constable George Hamilton along with Deputy Chief Constable Drew Harris and Assistant Chief Constable Mark Hamilton are all under investigation.
And he insisted he has no intention of stepping aside while the probe is ongoing.
Northern Ireland's two most senior police officers are under investigation for alleged misconduct in public office and criminality that could amount to conspiracy to pervert the course of justice.
The nine officers included the former West Yorkshire chief constable Mark Gilmore and former PSNI assistant chief constable Duncan McCausland.
The Belfast Telegraph reports that a number of less senior officers are also being investigated as part of the inquiry, which the Ombudsman's office described as a "critical incident".
The police ombudsman's inquiry into the matter would involve six independent investigators and the matter was a "serious incident" for the office of Dr Michael Maguire.
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It is understood the claims include allegations that police documents were altered.
Mr Hamilton said however: "I'm absolutely confident that there will not be misconduct established". "PSNI can confirm that a number of senior officers, including the Chief Constable and Deputy Chief Constable, have been informed of complaints made against them by former senior PSNI officers", said a spokeswoman.
"The complaints relate to allegations of misconduct by senior police during a criminal investigation by the PSNI into the two complainants, former senior colleagues, during 2014".
"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".
In its statement, the PSNI said that they would normally limit their responses on matters under investigation, but that in this circumstance, "this case has been the subject of recent speculative press and media coverage which has the potential to negatively impact on public confidence in policing".
Mr Hamilton was appointed chief constable in May 2014 - a month before the investigation into the vehicle contracts became public.
Mark Gilmore was suspended on full pay by West Yorkshire's Police and Crime Commissioner in June 2014 when news emerged of the investigation by PSNI into his relationship with a leading local vehicle dealership.
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