I really can't tell you much, I was looking for the same information before writing the diary, but rather unsuccessfully. All I know is that Siderov used to be a photographer in the National Museum of Literature. At this time, he joined the literature circle "39", and wrote a volume of poetry called "Autobiography". After the regime collapsed in 1989, he joined the Organization for Human Rights, founded by one of the Bulgarian dissidents. In 1990, he became the editor-in-chief of the newspaper of the UDF, "Democracy".

As to Borissov- true that he had a military background. You can take a look at his CV.

I can resist anything but temptation.- Oscar Wilde