Social media messages were behind the surprise resignation of police and crime commissioner (PCC) Jason Ablewhite from his £85,000 a year role.
The Independent Office for Police Conduct (IOPC) revealed that an investigation began after a member of the public came forward with screen shots of his posts.
The Independent Office for Police Conduct (IOPC) said tonight: "Initial information indicates the former PCC exchanged a series of messages with the adult member of the public last month through social media.
"IOPC oversees the police complaints system and investigates the most serious incidents and complaints involving the police. All our work is done independently of the police, government and interest groups.
"The IOPC oversight of PCCs is outlined in the Police Reform and Social Responsibility Act 2011, which states that we can only investigate the conduct of a PCC if there is an indication that a criminal offence may have been committed."
Earlier Dorothy Gregson, chief executive of the PCC's administrative team, said police had assessed the material to be "of a criminal nature".
Ironically part of her duties includes drawing the commissioner's attention "to any actual or possible contravention of law".
An interim PCC will be appointed on November 27 and will hold office until fresh elections are held, as scheduled, in six months time.
Three years ago Mr Ablewhite, during his campaign for election, was tackled about the perils and pitfalls of social media during a hustings meeting in Wisbech.
The forum, attended by over 100 people and which I chaired, drew out from Mr Ablewhite his Facebook posts from 2010 in which he had used the term 'pikeys'. He called it banter and said it was "pub time humour among friends".
Mr Ablewhite described critics attacking him over comments he posted on his Facebook page six years ago earlier as being "desperate to muck rack".
He was asked about "insults towards an ethic minority group" by an audience member. The other candidates responded before the microphone was passed to Mr Ablewhite.
"This is aimed at me," he said. "When we talk about muck racking and going back six years of Facebook page accounts, it shows how desperate some people are."
"I deal on a daily basis with some of the most vulnerable people in our society. In St Ives, we have a large Polish community, a large Bangladeshi community and a large Pakistani community yet that has never stopped us from having respect for each other."
He said people needed to differentiate "between pub time humour among friends that is not full of hate, not meant in that term whatsoever, and take politics out of it and think about what is going on instead."
One audience member told Mr Ablewhite "you were a public servant at the time (he was leader of Huntingdonshire District Council), paid out of the public purse; your mindset is racist. How can you say it is a bit of banter among friends?"
Mr Ablewhite replied: "Again you blow it out of all proportions. At the end of the day if people have taken offence then I am truly sorry."
He said that visitors to his home town of St Ives would find "hundreds of boards up for my election from Bangladeshis, Polish and Pakistanis. En masse they support me because they know what I have done for them. It as a simple as that."
His agent Debbie Clark was in the audience and rose to insist that the post on Mr Ablewhite's Facebook page was private and part of a private conversation.
She described it as "light-hearted banter" and someone had gone back six and a half years to find the post.
"I can honestly say I have called the Irish tinkers because that's what they are commonly known as," she said. "It does not mean I am not racist; my step son is Irish."
Councillor Steve Tierney said it was "despicable" Labour supporters had placed the question at the same time as their party was involved in an anti Semitic scandal.
Nearly 100 turned up for the hustings - the candidates agreed it was the largest turn out during the campaign, outnumbering audiences in Cambridge and Peterborough.
The National Alliance of Gypsy Traveller and Roma Women later called on the then chairman of the Conservative Party to suspend Mr Ablewhite pending investigation or an unequivocal statement condemning anti traveller racism and undertaking to treat all sections of the community equitably.
Cambridge Stand Up to Racism said: "We should never forget that gypsies were one of the main victims of the Nazi holocaust. Even today they are one of the most discriminated against groups in Europe".
They added: "As someone who is responsible for setting policing priorities we can have no confidence in his judgement or ability to do so without discrimination.
"The election of Mr Ablewhite has set policing in Cambridgeshire back years."
They said the use of the term 'pikey' was "deeply offensive. Such derogatory language risks reinforcing the marginalisation of this community, making them second class citizens".
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