Murder is illegal and an extremely grave crime.
Karmically, potentially not much. Genghis Khan's armies murdered millions. The jews through manipulating the occult have murdered over and over and largely avoided any form of retribution for mass negative karma so far.
But the unforeseen consequences of the future or knock-on effects (to others) are typically something low-level people can't understand. With either Black Magick or direct methods (the latter is a stupid and dangerous idea in any context), would you want to be a fool out of revenge, biting off more than you can chew?
Doing murder out of perverse reasons like 'fun', shekels or sexual sadism will often terraform a soul into something pretty ugly, pretty fast, even if it avoids the consequences of such an inscription. The jews can allay and tarry with this all they want, but they are still vile beings and are ultimately condemned.
Even if it is out of curiosity, it would help us if you were more specific about the misfortune. This is an anonymous service for a reason.
Who is the person that the spell or whatever targets? What's the intensity of the misfortune they perpetrated against you?