I did hear about this before. It happened long time ago probably before 1970, I guess. The murderer is a son of Sithon Kommadum, one of Lao leaders as well, who came from Southern part of Laos.
Someone told me when I was a Lycee boy that the then "Patheth Lao police concerned" wanted to punish the murderer to life sentence, but our Prince Souphanouvong did not want it. He said: "Other people's son is also my son, let's we better educate him than kill him". That was what I heard. Having first heard about the kindness of our late Prince, I then thought, no wonder all Lao people love him.
In addition, he(someone) just told me that the incident was not related to politic, but teenagers' stupidity.
It could be the case that they could not get along. I heard that most children of our leaders are really arrogant, especially if they are the northern people. You may hear about this as well that even ordinary Luangphabang people like to look down on southern people "Thai Tai". However, Thai Tai people are really proud themselves and hate people who look down on them. That is a teenagers' stupidity, I guess.
We all Lao people love and respect Prince Souphanouvong, who was, is and will be our Great leader.