Violence in thrillers - how much is too much

How much is too much violence in thrillers?

This is completely subjective, and will vary from author to author.  The use of violence is a tool.  Some writers (and this is not just with thrillers writers) have to show every blow-by-blow, every punch or kick or knife strike.  Then, there are others who show virtually no such specific action.

In order to do it right, violence must serve a purpose.  But, do not underestimate the power of the reader's imagination.  I recently came to grips with this on chapter 25 of my thriller Beholder's Eye.  The chapter centers around a teenage girl, who is kidnapped by a serial killer.  The chapter ends with her death.  During the first draft, I showed her very violent, very bloody death.  After thinking about it, I ended with the butcher knife being raised above the killer's head.  It would serve no purpose to show her death because we actually see a similar death in chapter 2--I don't need to show it again.

Also, I liked the way the chapter ended, because it leaves the reader wanting more.

Read some of your favorite authors.  How do they deal with violence?