Mr Aitchison said: 'I have received a letter from the director of social work, Les McEwan, in which he has offered to terminate his employment with the council.
'As chair of the child protection committee he helped put in place the first child protection guidelines in 1997 and the 1994 guidelines which were referred to by the inquiry team.
'Throughout his long and distinguished career, he has played a significant part in preventing children suffering harm.'
The following is an extract from Mr McEwan's letter of resignation:
'Having advised the council earlier this year that we needed to give first priority to finding the truth about what happened, I have been shocked and saddened by the full facts now available in the report into baby Caleb's death.
'As director I have ultimate responsibility for everything that happens in the department and as I said at full council I do not shirk that responsibility. I certainly do not in the case of Caleb.
While I played no part personally in any of the decisions taken regarding Caleb, indeed I was not interviewed by the inquiry team, I was, and I am part of the 'collective responsibility' which you referred to in your press statement and as director I shoulder that responsibility for social work.'
Mr Aitchison continued: 'I would wish to record the huge contribution which Les has made to the social work service in Edinburgh and the Lothians and in Scotland as a whole. It is typical of the man that he is putting the interests of the service before his own.
'We will continue with our urgent actions to address the findings and recommendations of the inquiry team's report. Steps have already been taken to ensure the day to day r unning of the department following Les' departure.'
The council did not comment on how soon a replacement director would be appointed or if anyone had been asked to temporarily stand in as the director.
Click herefor the full story in The Scotsman.