The public inquiry, chaired by High Court judge Lady Justice Thirlwall, is examining the circumstances surrounding Letby's crimes.
Peter Skelton KC, representing families of Letby’s victims said: “Child A was murdered on 8 June 2015. Is it your view that she [Letby] had murdered or assaulted children in your hospital prior to that date?
Dr Brearey replied: “I think that’s likely, yes.”
But he said nobody in the hospital had suspected Letby was harming children prior to June 2015.
The inquiry also heard the nurse had been redeployed from the hospital's neonatal unit to a clerical role in July 2016 after a series of babies had either died unexpectedly or come close to death during the previous year.
Consultants insisted Letby should be removed from nursing duties, the hearing heard.
After an internal grievance procedure lodged by Letby was upheld in her favour, though, the way was paved for her to return to nursing.
And, in January 2017, hospital bosses called the consultants to a meeting where chief executive Tony Chambers told them to apologise to Letby and her family.
At that meeting, head of nursing in the urgent care division Karen Rees then read out a statement from Letby.
Giving evidence at the public inquiry in Liverpool, Dr Brearey said: “The whole meeting felt choreographed and Karen Rees was quite dramatic in her reading of it.
"We were all quite stunned - as a synopsis of executive behaviour I can’t imagine an example of anything more incompetent in the history of the NHS.
"How you can start a meeting saying you follow ‘Speak Out Safely’ practices and then tell all seven consultants that have significant concerns that they have to apologise to the person? And that she would be going back to work or else there would be consequences?
"It was quite striking and surprising and upsetting for most people there."