Once a lawyer takes a case, he tries to finish it. I haven't looked at Croatian law, and I haven't really invested much time into finding just the "right" quote. But here's a snippet of U.S. rules on ethically declining or terminating representation:
 A lawyer may withdraw from representation in some circumstances. The lawyer has the option to withdraw if it can be accomplished without material adverse effect on the client's interests. Withdrawal is also justified if the client persists in a course of action that the lawyer reasonably believes is criminal or fraudulent, for a lawyer is not required to be associated with such conduct even if the lawyer does not further it. Withdrawal is also permitted if the lawyer's services were misused in the past even if that would materially prejudice the client. The lawyer may also withdraw where the client insists on taking action that the lawyer considers repugnant or with which the lawyer has a fundamental disagreement."