The Nisman case is taken straight from a murder mystery novel, so it's not very surprising that it would get a TV series.

My personal theory is that it was a forced suicide (as in someone told him, "kill yourself or you'll wish you had"), but who may have ordered it, I have no clue. Former president Cristina Kirchner gets a lot of flak for allegedly placing the hit - the fact Nisman was going to testify against her on an election year doesn't help matters - but offing enemies is not her style, she would rather use her influence to discredit them.