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.

Now, the book "Tiglachin" is his new work. The name "Tiglachin" sounds like it might be Amharic or another Ethiopian language. I should verify the possible meaning. Maybe it's a symbolic term or refers to a specific period. Since the book is released in 25 installments, it could mean it's a serial publication, each installment covering a chapter or a theme. The PDF format suggests it's accessible online, maybe through the internet or some digital platform, especially since Mengistu might be in exile and can't distribute books in Ethiopia legally.

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.

The story could end with the book's reception after all 25 installments are released, any follow-up actions, and how it's received in academic and political circles. Perhaps some historians start using it as a source, while others criticize it as self-serving.

Possible elements for the story: Mengistu, in exile, working on the book, the process of writing, any challenges faced (like lack of resources, censorship issues), reactions from family or associates, legal implications if the book is controversial, and the impact on Ethiopian politics. Maybe the Ethiopian government's response, either through legal actions or public statements.