Good point. Fortunately enough, Peter tells us in 2 Peter 1:20 that:
Above all, you must understand that no prophecy of Scripture came about by the prophet's own interpretation. For prophecy never had its origin in the will of man, but men spoke from God as they were carried along by the Holy Spirit.
If this clown DID think he heard Jesus (which imho is incorrect theologically--the post-ascension interaction of the Trinity with us is via the Spirit, not Jesus) telling him to kill someone, he's supposed to take it up with a spiritual elder, who can say "yeah, that meets with what the Bible says about killing preachers and their kids" or "uh, stay here in the office...I need to make a phone call to the police." It should be clear to others. BTW: this idiot couldn't even get his excuses straight. The biblical model for doing what he did is "the Devil made me do it", not Jesus.
God used/uses his prophets to instruct, teach, warn and minister to his people. I'm not sure that he ever used a prophet to kill someone.