The President's Murderer - after reading

I read "The President's Murderer" and here is my answer for after reading# 6.

I think that the army killed old President. They did not like his political strategy and wanted to change the President so that they could control the country as they like. Therefore, old President was killed by them, and their very good friend became new President.

This is just my guess. I would like to know the author's answer. I am also interested in who Marta was.