The police watchdog has described the comments of a South Yorkshire police chief constable about the Hillsborough disaster as "at best ill-judged and at worst offensive and upsetting".
Chief constable David Crompton sent an email to his senior staff in preparation for South Yorkshire Police's response to the publication of the Hillsborough Independent Panel's report last year.
Crompton's email implied the Hillsborough Campaign for Justice group were not telling the truth about the 1989 disaster.
The email read: "One thing is certain - the Hillsborough Campaign for Justice will be doing their version ... in fact their version of certain events has become 'the truth' even though it isn't!!
"I just have the feeling that the media 'machine' favours the families and not us, so we need to be a bit more innovative in our response to have a fighting chance otherwise we will just be roadkill."
Last month, the police and crime commissioner of South Yorkshire, Shaun Wright, wrote to the IPCC when he was made aware of the emails and associated documents.
But IPCC commissioner Nicholas Long said the majority of the emails and documents he considered "raises no issues". However, he said one email from the chief constable "caused me concern".
He said: "It referred to preparing what 'amounts to the case for the defence' and stated that the 'Hillsborough Campaign for Justice's ... version of certain events had become the truth even though it isn't'.
"I consider that this is at best ill-judged, and at worst offensive and upsetting. I have written to Chief Constable Crompton to express these views. Families and individuals affected by the Hillsborough tragedy, along with the wider public, will rightly be concerned over the apparent attitude displayed by this communication within the highest ranks of the force which is currently under investigation in relation to the actions of its officers and staff around the disaster."
Mr Long added that while "these emails have serious implications for public confidence" they do not amount to recordable conduct and the IPCC does not require a formal referral.
In response Mr Crompton said: "It was never intended to cause any offence and I apologise if it has done so. Nor was it intended to challenge the integrity and views of those who lost loves ones in the Hillsborough disaster."
The report's publication provoked widespread condemnation of the police's response to the disaster at Sheffield Wednesday's ground in April 1989 which left 96 Liverpool fans dead. It also revealed that police statements had been altered so the authorities would be portrayed in a better light.
The police and crime commissioner for South Yorkshire police, Shaun Wright said he was disappointed with the language and had raised his concerns with Crompton.
He said: "I accept the chief constable's regret for his language in this one particular email and his apology."
Information from the Press Association was used in this report.