Who could have done the massacre??

1. India with the help of Nepali political party like Nepali Congress: India has always seen Nepal as a " Bato ko Kanda", it made sense for India to get rid of the Monarchs to turn Nepal into a leaderless nation by destroying the sense of unity.

2. Political Parties with the help of Royal Insider: NC always saw monarchy as an obstacle and Maoists had declared Monarchy as their enemy...they were both fighting Monarchy in their own way.

3. Paras/Gyanendra with the help of India or political parties: For the lust of being a king themselves

4. Dipendra's insanity.

Out of all the reasons i have listed above...Dipendra's insanity is least likely of all to have caused the massacre in my opinion.