Role in the case
As Senior Investigating Officer, Wenham led the investigative scoping decisions: which deaths to treat as potentially suspicious; which experts to instruct; which material to retain and test forensically; which to treat as peripheral. The investigative frame established in 2017-2018 shaped the 2020 charging decision, the 2022-2023 trial, and the 2024 Child K retrial. Independent analysts have argued the investigation adopted a suspect-first orientation from early in its scoping; the Hummingbird whistleblower report (December 2025) specifically addresses this.
The suspect-first scoping question
A live post-conviction question is whether the Hummingbird investigation systematically considered natural-cause and viral-outbreak differentials before narrowing onto a deliberate-harm hypothesis centred on Ms Letby. The absence of SUDI/SUDIC-standard evidence collection at the time of each death means that the retrospective investigation worked at significant informational disadvantage, which makes scoping decisions evidentially load-bearing. Wenham’s Thirlwall evidence and police case papers are the primary sources on these decisions.
Dr Evans’s instruction
Dr Dewi Evans self-referred to Cheshire Police in 2017 offering his services as a neonatal expert witness. The decision to instruct him was taken at SIO level. The full correspondence trail between Evans and the Hummingbird investigation has not been made fully public; parts have surfaced through the Thirlwall document discovery.
Read alongside
- Transcript: DCS Wenham Thirlwall evidence
- Operation Hummingbird overview
- Hummingbird whistleblower report digest
- Analysis: suspect-first scoping
- Analysis: Hummingbird scope decisions
- Analysis: the seven-year delay problem
- Dr Dewi Evans — prosecution causation expert
Source
Thirlwall Inquiry evidence bundles; Cheshire Constabulary public statements; Operation Hummingbird briefings; Chester Standard contemporaneous coverage.