Last week, an official report released in Kigali claimed that Nzirorera, at the time Secretary General of the then ruling party, co-organized Juvénal Habyarimana's assassination with fellow Hutu extremists.
Nzirorera's Lead Defence counsel Peter Robinson urged the International Criminal Tribunal for Rwanda (ICTR) "to amend the indictment to add the charge of planning the assassination of President Habyarimana".
"Nzirorera strictly denies that he is responsible for the assassination of President Habyarimana", he added.
For the Office of the Prosecution, American Counsel Don Webster replied that he didn't "have anything to say" prior to being notified a written request to modify the indictment.
Chief of the Prosecution Hassan Bubacar Jallow has reiterated on various occasions in the past that investigating Habyarimana's death was not part of the ICTR's mandate.
Defence lawyers strongly disagree. They contend that the Rwandan Patriotic Front (RPF), the former rebel movement led by President Paul Kagame which seized power in 1994, is responsible for killing Habyarimana.
The shooting down of the presidential plane triggered off the Rwandan genocide which, according to UN figures, cost the lives of 800,000 civilians, mostly ethnic Tutsis but also moderate Hutus.
© Hirondelle News Agency