From an Islamic standpoint, that is was Qadri stated he was acting upon, he was guilty.
1. He killed a man he swore to protect. If he was to break his oath he should have proclaimed it, and stopped guarding the governor. He instead hid it, and shot him in the back.
2. If he had a dispute regarding something the governor said, he should have filed a court case, or at he very least bought it in front of a panel of Qadis, from all Fiqhs (Barelvi, Deobandi. Ahle Hadith, Shia) to determine whether there was a genuine case. He didn't, and shot the man in cold blood. He wasn't even given a chance to explain his side. In Islamic fiqh even apostates are asked to explain why they have left the deen.
3. He broke the sovereign laws of a nation and was completely unrepentant.
I say this as someone who hails from the Barelvi school, he was wrong, and his supporters are misguided beyond belief.