Complex sentence: As the nature of the third life and the necessary procedure was unknown to humans, it appeared to the human population that Pipo and Libo were brutally murdered, thus the main and first reason that Ender came to Lusitania.
Split into simpler sentences: As the nature of the third life and the necessary procedure was unknown to humans, it appeared to the human population that Pipo and Libo were brutally murdered. Thus the main and first reason that Ender came to Lusitania.