SAN FRANCISCO — The California State Bar suffered a setback last week in its misconduct case against Del Norte County district attorney Jon Alexander when a key witness refused to testify, but it’s still moving ahead with the most serious charge against him.

Bar prosecutors will rely on a recording they say shows Alexander had an improper conversation with a criminal defendant outside the presence of her lawyer, a bar spokeswoman confirmed. The defendant, Michelle Taylor, surprised bar prosecutors by refusing to testify late last week during their second deposition attempt, despite a deal with the state attorney general’s office that was supposed to secure her cooperation.