LONDON — Lawyer for convicted British killer nurse Lucy Letby said Monday he plans to ask an appeals court to review his convictions after the prosecution’s lead expert changed his mind about how three babies died.

Lawyer Mark McDonald said Dr Dewi Evans could no longer be believed after overturning his opinion that Letby injected air into a nasal gastric tube which killed three infants.

“I have new evidence that casts doubt on the conviction,” McDonald said. “The defense will argue that Dr. Evans is not a reliable expert, and given that he was the prosecution’s lead expert, we say all convictions are unsafe.”

Letby, 34, is serving multiple life sentences with no chance of release after being convicted of murdering seven babies and attempting to murder seven others while working as a neonatal nurse in Countess of Chester Hospital, in the northwest of England, between June 2015 and June 2016.

McDonald said he will file a motion this week asking the Court of Appeals to reconsider his appeal request. The court twice rejected Letby’s appeal request.

Letby, who testified at two trials that she had never harmed a child, has always maintained her innocence.

A an investigation is currently underway to examine the hospital’s failures to understand why babies were dying in the neonatal unit and why it took so long to stop Letby.

The Crown Prosecution Service did not immediately respond to a request for comment on the McDonald’s allegations.