Context
Cheshire Police’s Operation Hummingbird was the investigation that produced the Letby charges. This page collates the public-record procedural chronology from the May 2017 opening of the investigation through the 2024 Child K retrial conviction.
Chronology
- May 2017. Cheshire Police open Operation Hummingbird under then-DCS Nigel Wenham. Investigation is scoped from the outset on the “another Allitt” framing received from the Trust executive briefing. See our Allitt framing analysis.
- 2017 onwards. Dr Dewi Evans approaches Cheshire Police offering his services as an expert. He is subsequently instructed as lead causation expert.
- 3 July 2018. Letby is arrested at her home in Chester for the first time. Interviewed under caution. Denies the allegations.
- June 2019. Second arrest. Interviewed under caution. Consistent denials.
- November 2020. Third arrest and charge. Interviewed under caution. Consistent denials. CPS charges: 8 murders, 10 attempted murders (later amended).
- October 2022. Trial begins at Manchester Crown Court.
- August 2023. Convictions: 7 murders, 7 attempted murders. Whole-life order imposed.
- June–July 2024. Child K retrial. Conviction and second whole-life order.
- July 2025. Three former Countess of Chester executives arrested on suspicion of gross negligence manslaughter in connection with the deaths Letby was convicted of.
What the chronology shows
Three arrests were required before CPS charging. Across all three, Letby denied the allegations consistently. The charge eventually proceeded on the basis of the Evans causation opinion, the shift chart, the insulin assay, the notes and the digital evidence — not on any admission.
The subsequent arrest of three former executives in July 2025 is evidentially significant. Cheshire Police’s own investigative work eight years after the cluster identified the executives’ role as a distinct criminal question. That finding is consistent with the institutional-failure reading the Thirlwall Inquiry has documented and the post-conviction independent-expert evidence has elaborated.
Read alongside
Hummingbird scope decisions, The Allitt framing effect, DCS Wenham Thirlwall testimony, Anonymous Hummingbird whistleblower report.