I need to make sure the information is accurate regarding Mengistu's history. For example, he was ousted in 1991, not in jail but in exile. His health is a concern he's been in the news for, so if the book is recent, that might affect his ability to write. But assuming the book is released now, his health could be a factor in his decision to write.

I should also consider the historical and political context of Ethiopia around the time of the Derg regime. The Ethiopian revolution in 1974, the fall of Haile Selassie, the rise of Mengistu, the Mengistu era's policies, the Eritrean conflict, the famine, the Red Terror, and the eventual fall of his government in 1991. The book might address these events.

Since the user mentioned the "25 install" in the query, the structure of the book being released in 25 installments is a key point. Each part might build a story or argument, creating a serialized narrative that keeps readers engaged. This approach could be strategic to maintain interest and spread the content over time.

I should also consider any possible collaborations or individuals involved in the book's production. Maybe exiled Ethiopian writers, translators, or publishers in countries where he's granted asylum. The process of writing, editing, formatting as a PDF, and distributing it.

In terms of structure, a detailed story could be broken into sections: Introduction to Mengistu, the context of his exile, the significance of the book's title, the format (25 installments), the content overview, public and governmental responses, analysis of the content's credibility, and the legacy of the book in Ethiopian history.

Also, considering the diaspora's role. Many Ethiopians in the diaspora might have strong opinions about Mengistu, depending on their backgrounds—some might support him, others would oppose. The book's release could polarize these groups.

Potential challenges in writing this story include avoiding bias, accurately representing both sides of Mengistu's legacy. It's important to present the Ethiopian government's perspective on his regime and the opposition's view, as well as his own narrative.

In terms of narrative flow, starting with Mengistu's background, the announcement of the book, the initial reactions, the content of the book, the evolution of public opinion as the installments are released, and the aftermath.