A children’s nurse who was arrested nearly a year ago on suspicion of murdering eight babies and attempting to kill a further six is now suspected of trying to murder another three infants.

Lucy Letby, 29, was initially arrested last July as part of a major police inquiry into the deaths of 17 babies at the Countess of Chester hospital. She was subsequently bailed pending further inquiries.

It is understood she was rearrested on Monday on suspicion of murder in relation to the deaths of eight babies and the attempted murder of six babies. She has also been arrested in connection with the attempted murder of three additional babies.

DI Paul Hughes, of Cheshire constabulary, who is in charge of the investigation, said the woman – whom police have not named but is understood to be Letby – was in police custody helping officers with the case.

Police were conducting searches at her home in the Blacon area of Chester on Monday, with a blue forensic tent positioned at the front of the semi-detached property.

The investigation is the first major police inquiry into child deaths in UK hospitals in nearly 30 years. It was launched two years ago following an unusually high number of deaths and non-fatal collapses in the Countess of Chester’s neonatal unit.

Detectives are investigating the deaths of 17 babies and 16 non-fatal collapses between March 2015 and July 2016.

Letby, originally from Hereford, had worked at the hospital for seven years and was training to work with babies in intensive care when she was detained last July. It is understood she was suspended a year earlier and before this she had been removed from clinical duties and placed in an administrative role.

In a 2013 interview with the Chester and District Standard newspaper, the nurse said she cared for babies requiring various levels of support. She had worked at the unit as a student nurse during three years of training before qualifying as a children’s nurse at the University of Chester in 2011.

Hughes said: “I would like to reassure people that we are doing everything we can as quickly as we can to identify what has led to these baby deaths and collapses. Due to the nature of this investigation it is extremely challenging but it is important to remember that it is very much active and ongoing – there are no set timescales and we remain committed to carrying out a thorough investigation as soon as possible.

“We fully appreciate that it continues to have a big impact on all those involved, including the families of the babies, staff and patients at the hospital as well as members of the public.

“Parents of all the babies are continuing to be kept fully updated and are being supported throughout the process by specially trained officers. This is an extremely difficult time for all the families and it is important to remember that, at the heart of this, there are a number of bereaved families seeking answers as to what happened to their children.”

Susan Gilby, the chief executive of the NHS trust that runs the Countess of Chester hospital, said: “Our thoughts are with the bereaved families, we are cooperating fully with the ongoing police investigation and so are unable to comment further at this time.”