Complex sentence: Like many serial killers, Dexter keeps a trophy of each kill, by cutting his victim's cheek with a scalpel and collecting a drop of blood, which he preserves on a blood slide.
Split into simpler sentences: Like many serial killers, Dexter keeps a trophy for each kill. Before dispatching a wrongdoer, Dexter makes an incision on his victim's cheek with a scalpel and collects a blood sample, which he preserves on a blood slide.