Seems to me that if Kasey wasn't paid the amount agreed upon, then they pretty much voided the agreement... at which point Kasey could have taken the site down until the agreed amount was paid. Repossession is a legal action.
As for the vandalism bit.. The design, not being paid for in full, still belongs to Kasey. Ya can't vandalize your own property.
That's how I see it.. Then again, I like chocolate chip celery..
