Detectives have arrested a senior hospital boss on suspicion of perverting the course of justice in connection with the inquiry into killer nurse Lucy Letby.
Cheshire Constabulary said a search warrant was carried out at a property on Wednesday.
A person was arrested and later bailed, pending further inquiries.
In July 2025, three members of the leadership team at the hospital, who occupied senior positions between 2015 and 2016, were arrested on suspicion of gross negligence manslaughter.
It is understood that the suspect arrested on suspicion of perverting the course of justice was one of the three arrested last year.
Letby, 35, is the most prolific child serial killer in Britain.
She is serving 15 whole-life orders after she was convicted at Manchester Crown Court of murdering seven infants and attempting to murder seven others between June 2015 and June 2016.
The babies were attacked by various means while Letby worked as a nurse on the neonatal unit at the Countess of Chester Hospital.
There have been mounting calls for a retrial as the 36-year-old’s legal team has raised major questions about the safety of her convictions.
Amanda Knox recently released a podcast about her case, entitled DOUBT: The Case of Lucy Letby.
Netflix has also released a documentary, called The Investigation of Lucy Letby.
In a statement issued on Thursday, police said: “On Wednesday 22nd April officers from Cheshire Constabulary executed a search warrant at a property in connection with Operation Duet.
“Operation Duet is the ongoing investigation into corporate manslaughter and gross negligence manslaughter at the Countess of Chester Hospital.
“An individual was arrested on suspicion of perverting the course of justice. They have subsequently been bailed pending further enquiries.
“The searches at the property have now concluded.
“Both the corporate manslaughter and gross negligence manslaughter elements of the investigation are continuing and there are no set timescales for these.”
The corporate manslaughter probe was launched in October 2023 and the gross negligence manslaughter probe launched in March 2025.
Police said at the time they were focusing on the “grossly negligent action or inaction of individuals”.
In 2023, the doctor who first raised the alarm over Letby called for NHS managers to be held accountable for ignoring concerns that he raised in July 2015.
Lead paediatric consultant Stephen Brearey called for hospital managers to be regulated in the same way as doctors and nurses.