The Vanished Man by Jeffery Deaver 

A trained Magician, Malerik, is killing people by performing escape tricks with them in the title role.  He does the Lazy Hangman, where the victim strangles herself.  Two policemen happen upon the scene, but the magician escapes using illusion and quick change.  Lincoln Rhyme is asked to help solve the case and he recruits an aspiring magician, Kara, who can explain how it was done.  The next victim is involved in Sawing the Woman in Half trick.  Trace evidence leads from one crime to the next.  The real target is a circus in town which is where Malerik was scarred from a trick gone horribly wrong.  Lincoln and Kara manage to trick the magician and capture him.