I might add that any "honor killing" necessarily involves malice aforethought. It is capital murder. Punish it swiftly to discourage others from following his example.
When some Hindu "holy men" explained to their British occupiers that suttee (burning widows on their husband's funeral pyre) was a deeply entrenched custom, the Brit governor said, "We also have a custom. It is our custom to hang those who murder innocent people. So, go ahead and build your pyre. We will build a gallows next to the pyre. Then, you practice your custom, and we will practice our custom."
Suddenly, suttee when out of fashion!