Philip Sugden

Context:

Described as 'really the definitive survey of the case' and referenced multiple times throughout the episode as a key source for information about Jack the Ripper suspects

Context:

Referred to as 'whose book on the Jack the Ripper case is the definitive history' - discussed as an authoritative source on the Jack the Ripper murders

Context:

Described as 'the definitive book' on the Ripper case and 'by far the most scholarly and sort of serious book on this.' The hosts reference it multiple times throughout the episode for expert analysis on the murders, witnesses, and suspects.