Complex sentence: Alexander Petrov is a criminologist working for the Keystone City Police Department, but in order to advance his career, he uses one of the weapons that Albert Desmond used as Mister Element to freeze the lab supervisor solid.
Split into simpler sentences: Alexander Petrov is a criminologist working for the Keystone City Police Department. But in order to advance his career, he uses one of Albert Desmond's weapons used as Mister Element to freeze the lab supervisor solid.