Spoiler warning: Plot and/or ending details follow.
A child at the time of the massacre, Shannon later found her mother Eliana reluctant to talk about the massacre in any detail. Shannon wrote the book in part to help her understand the motivations of then Governor Adrian Kodos's decision to have 4,000 colonists killed, and the motivations of those who followed him. Her mother agreed to talk to her about the crisis for Shannon's book.
Shannon was able to interview a number of individuals, including Alexander Simmons, Donovan Eames, Hisayo Fujimura, and Starfleet Captain Philippa Georgiou. Shannon reached out to Captain Gabriel Lorca to ask him for an interview, however he declined her request. (DSC novel: Drastic Measures)