Complex sentence: According to the official version, Alekseychik was fired from his natural gas technician job several days prior to the explosion, and to get even with his former employers and the city he sabotaged the gas system thus causing the tragedy.
Split into simpler sentences: According to the official version, Alekseychik was fired from his natural gas technician job several days prior to the explosion. To get even with his former employers and the city he sabotaged the gas system thus causing the tragedy.