London Mayor Ken Livingstone showed "unusual insensitivity" by comparing a Jewish reporter to a Nazi concentration camp guard, a tribunal has been told.
Mr Livingstone did not attend the hearing
Mr Livingstone is accused of bringing his office into disrepute after being tape recorded making the comments to Oliver Finegold in February.
The disciplinary tribunal was told the Evening Standard reporter was left "shocked and offended".
The mayor maintains he never meant to offend Jewish Londoners.
The hearing has now been adjourned for a date to be set in mid to late January.
The case was brought against him by the Standards Board of England to decide if he had breached the Greater London Authority code of conduct.
If found guilty by the Independent Adjudication Panel for England, Mr Livingstone could be banned from office for five years, face suspension, or undergo training.
The incident happened when Mr Finegold approached Mr Livingstone outside a party at City Hall and Mr Livingstone asked him whether he had ever been a "German war criminal".
Discovering that Mr Finegold was Jewish, the mayor likened him to a Nazi concentration camp guard, the tribunal heard.
Tim Morshead, for the panel's Ethical Standards Officer, asked members to note that in Mr Livingstone's own view, the Holocaust was one of the worst reference points for evil.
The mayor refused to apologise to Oliver Finegold
He said: "After being told that Mr Finegold was a Jew what he proceeded to say could hardly have been more offensive.
"What made it reflect on his office and authority was that the comparison was made to a man that he knew to be Jewish and compared to wartime Germans."
But Tony Child, for Mr Livingstone, stressed that the mayor had never meant to offend Jewish Londoners by the words he used.
His outburst had been triggered by his dislike of Associated Newspapers and their support for anti-Semitism, the tribunal heard.
He said: "An apology may be relevant to mitigation but a lack of an apology cannot determine liability."
Mr Livingstone did not attend the third day of the hearing at the Aeonian Centre in central London.