Part of the "Costak" preproduction involves planning the visual style of the murders. The passion or the reason involved in the murder seems more to the point than blood being spilt everywhere. "Costak" is not about gore but things that might terrify us beyond gore. What helps in this view is the method used by Petri. Most of Petri's murders are committed with a knife to the heart. A side benefit to a murder like this is less blood squirting out since heart almost immediately stops pumping blood.
A found this tidbit in a book called "Mobspeak".
Mobspeak: The Dictionary of Crime Terms (Paperback) by Carl Sifakis
352 pages Checkmark Books (September 2003) ISBN: 0816045496