The murders were a false-flag attack instigated by Xenu to kill his enemies, cleanse the planets of people that he considers "undesirable" and to provide a pretext to take greater control of the Galactic Defence Force.
After having glanced through what I can only describe as one of the worst screenplays I've ever read, I think I've found the section you're referring to;
- Xenu's GDF troops (led by their psychiatrist officers) evacuate; "all citizens who are in the Field of the Arts, education, Journalism, religious leaders, civil liberty activists, or those who are unemployed" from the planet Procyon and transport them to the planet Teegeeack.
- They collect troops that are loyal to the government and transport them to the same planet.
- They use a "451 MX EXPLOSIVE DEVICE. The most powerful atomic bomb ever made" to blow them all up, then blame the Grey Invaders;
"News Reporter : This is truly a sad day. We are just receiving breaking news from the
Galactic Defense Force that Teegeeack has just suffered a full scale
assault from the Grey invaders. Resulting in the death of Commander
Rawl, leader of Teegeeack.
Xenu is said to be distraut [sic] after learning of Rawls death and the
attack on Teegeeack and has sworn to redouble his efforts to defend
the Confederation.