Continuity of evidence

Continuity of evidence becomes a test of assumptions when Peter Diamond examines the paper bag bearing handwritten lists. He asks not merely what the lists suggest, but where the bag came from and how it passed between people. Its route can be traced; its origin and authorship cannot be taken for granted. That distinction unsettles the apparent solution and makes Jessica Shaw, rather than Sid Towers, the person Diamond presses to explain the lists.

The evidentiary question

Diamond introduces the principle while speaking with Julie Hargreaves after more than thirteen hours on duty. Julie has assumed that Sid made the lists. Diamond challenges that assumption by treating the paper bag as evidence to be passed to the Crown Prosecution Service, which, in his account, will want to know where it originated. The exchange shifts attention from what the lists appear to mean to the history of the object carrying them.

That shift matters because the bag seems to support a compelling story about Sid. If he wrote the lists, Diamond reasons, it was natural to imagine him as the writer of the riddles, the person who stole the Penny Black, and the one who somehow entered a locked boat. The lists looked like working notes for a riddle that never appeared, perhaps because Sid was killed before finishing it. But resemblance and narrative fit do not establish authorship. Diamond acknowledges that he made a mistake by accepting the attractive explanation too readily.

An origin that cannot be assumed

Julie suggests a secondhand bookshop as the bag’s source. Diamond will not accept that as certain: many shops could have supplied it, and the fact that the bag contained a book does not establish where the bag itself came from. Even identifying Sid as the book’s owner leaves a gap. The book might have come from another collector, perhaps someone else in the Bloodhounds who wrote lists on a paper bag.

That possibility opens more than one route into Sid’s possession. The bag might have reached him accidentally or by design; neither possibility is settled in the exchange. The uncertainty is consequential because a known owner of the book is not necessarily the maker of the lists, and an object found with a person does not by itself tell Diamond who first created or handled it. The principle therefore works here as a demand for a documented chain, not as a shortcut from possession to guilt.

From custody to suspicion

Diamond supplies the chain he can establish: the bag was Sid’s, Sid handed it to Jessica, and Jessica handed it to Diamond. When he lays out that sequence, Jessica gives a reluctant sigh, conceding the logic of what he has said. The chain accounts for the bag’s passage through their hands, but it does not directly show who wrote the lists. Diamond’s next step is an inference: if Sid did not write them, Jessica did.

He makes that inference explicit by naming Jessica his prime suspect. The reasoning is conditional, not a claim that the chain itself proves authorship. Diamond has first entertained the possibility that the lists belonged to Sid; once he withdraws that assumption, Jessica becomes the alternative author within the account he presents. The bag’s passage from Sid to Jessica and then to Diamond gives that alternative a concrete evidentiary path, while the unresolved earlier provenance keeps the question open.

A principle and its limits

Diamond describes continuity of evidence as important to what prosecutors need to know, but his own explanation also reveals the limits of the chain. It clarifies who passed the bag to whom; it does not settle whether Sid acquired it from a shop, a collector, or another Bloodhounds member, nor whether the lists were written by Sid or Jessica. Keeping custody and authorship distinct prevents the physical history of the bag from being mistaken for a complete account of its contents.

The principle also changes the tone of Diamond’s conversation with Jessica. He says the discussion is not a formal interview and presents his accusation as a way of giving her an opportunity to explain. His claim that she is his prime suspect is, by his own admission, an exaggeration intended to get through to her. Continuity of evidence thus serves both as a method of checking a detective’s assumptions and as the structure of a pointed, informal challenge: the sequence of handovers is clear enough to demand an answer, while the decisive question of who made the lists remains to be explained.