Giving evidence, Dr U said that he believed that Letby had been struggling with her mental health and struggling to sleep because of worry and anxiety.
The doctor was asked why he had supported Letby when she raised a grievance process against the hospital, rather than his consultant colleagues who were voicing their worries about her.
The doctor said: “I wasn’t aware of the full clinical picture and I provided support by being misled and maybe manipulated, and for that I’m really sorry that things have come to the end as they have.
“I have a lot of regrets about how that period of time took place.”
The hearing was told that in one message, Letby inquired about the condition of Child N, an infant she attempted to murder in early June 2016, and queried with the medic, referred to as Dr U, whether she had done anything wrong.
The inquiry heard Dr U messaged back: “Oh Lucy, poor little thing. I am sure he has had the best care possible and you will have done everything you could for him.”
Earlier, another consultant told the inquiry that senior directors “actively bullied and victimised” doctors when they raised suspicions about the nurse.
The paediatrician, who has been anonymised by a court order, told the public inquiry that hospital directors “wanted us to shut up” about their concerns over Letby.
Referred to as Dr ZA, she said she feared her job was on the line.
But Dr ZA told the inquiry that by 2017 she felt she “could not live with herself” if she did not keep pushing to have Letby removed from her post.
She said in hindsight the rising number of unexpected deaths and collapses of babies from June 2015 reminded her of “the analogy of a frog in boiling water where you slowly turn the heat up”.
She told the Thirlwall Inquiry at Liverpool Town Hall: “You don’t realise at the time, because it is a gradual increase, how dramatically things are changing.”
Dr ZA said she “deeply regretted” dismissing the possibility that one of the babies Letby was later convicted of poisoning with insulin had been deliberately harmed.
The paediatrician said she was confused by blood test results that showed Baby F, who died in August 2015, had high levels of insulin but low levels of a chemical called C-Peptide, which is released by the pancreas when it produces insulin.
The inquiry and Letby’s trial both heard that if the ratio between the two is off it can indicate insulin has been administered from outside the body, but by the time she saw the results his blood sugar levels had returned to normal so she did not order a repeat of the test.
Dr ZA said while the possibility of deliberate harm crossed her mind, she dismissed it.
She said: “It just seemed so fantastical and unlikely that it couldn’t possibly be what had happened.”
