What “scoping” means
When a major crime investigation opens, senior investigators make a series of early decisions that shape everything that follows. What is the investigative hypothesis? What time period does the inquiry cover? Which cases are in scope, which are out? What expert instruction is needed? Who instructs the experts? What weight will the investigation give to competing hypotheses? These decisions are called scoping. They are usually made by senior officers in the first days and weeks of an inquiry.
Scoping decisions in a major criminal investigation are not routinely second-guessed. But because they are the foundational decisions on which everything else rests, they are appropriate subjects of post-conviction review, particularly where the evidence has subsequently shifted materially.
The information the police received from the Trust in May 2017
When Cheshire Police were contacted by Trust executives in May 2017 — eight months after the consultants’ September 2016 letter — the information the police received was substantially filtered. The anonymous 150-page Hummingbird whistleblower report (see our summary) documents that the initial briefing framed the cluster as a possible “another Allitt” case. It did not systematically present the alternative explanations — the superbug outbreak, the sewage and plumbing failures, the doctor shortages, the unit-designation mismatch — with the same prominence.
This is not an accusation that the executives deliberately misled police. It is a description of the information-asymmetry problem: the executives had their own interest in the frame under which the investigation would operate. The frame that emerged was the frame that served the executives’ institutional position at the time.
The key scoping decisions
- Adoption of the suspect-first frame. Hummingbird’s scope focused on Letby’s presence at specific events rather than on a systematic analysis of what killed each baby with a blinded differential-diagnosis review first. This is a scoping choice with material consequences.
- Time window selection. The events selected for investigation were the ones occurring within the period when the cluster was most concentrated and when Letby was working. Events before that window and events on shifts she did not work were not the focus.
- Expert instruction. Dr Dewi Evans was instructed early in the investigation. His methodology — forensic rather than differential-diagnosis — was compatible with the suspect-first frame. A scoping decision to instruct an expert applying a modern UK neonatology differential-diagnosis methodology would have produced a different evidentiary picture.
- Non-instruction of systems-failure experts. An investigation scoped to consider whether the cluster was explicable by a combination of outbreak, staffing, infrastructure and acuity would have instructed paediatric infection-control experts, NHS patient-safety experts, and neonatal-network commissioning experts. Hummingbird did not.
- Exhibit retention. Scoping decisions determined what physical material was retained and what was not. TPN bags were not retained. Post-mortem radiology was not systematically obtained with a view to forensic air-embolism analysis. NG-tube equipment was not sequestered. These exhibit-retention gaps are functions of the scoping frame.
- Sample-handling protocols. The insulin samples were processed under clinical rather than forensic laboratory protocols. A scoping decision to treat the samples as forensic evidence from the outset would have required the samples to be sent to the Guildford forensic lab, not to Royal Liverpool.
Why this matters now
The scoping decisions made in May 2017 constrained what could be investigated and what could be used as evidence at trial. Some of these constraints are now irreversible: TPN bags cannot be re-created, forensic-standard insulin samples cannot be retrospectively obtained. Other constraints can be revisited: post-mortem material has been preserved in some cases and can be re-examined; the clinical record can be re-read with a proper differential-diagnosis frame.
The October 2025 CCRC application, supported by thirty-one-plus independent expert reports, is effectively a request to the CCRC to re-examine the case under a scoping frame different from the one Hummingbird adopted in May 2017. The Panel’s review is the alternative scoping frame in action: differential-diagnosis-first, systems-failure-informed, independent of the Hummingbird investigative hypothesis.
What the Thirlwall Inquiry adds
The Thirlwall Inquiry evidence of former DCS Nigel Wenham (see our summary) addresses how Hummingbird was scoped from his perspective. It does not reach the conclusion that the scoping was wrong; Thirlwall is an institutional inquiry, not an appeal. But the evidence places on public record how the scope decisions were made and by whom, which is material the CCRC did not have at the time of the original investigation and trial.