SAN DIEGO — In June 2019, a 30-year-old Utah man allegedly robbed five San Diego-area convenience-store clerks at gunpoint during a 29-hour crime spree. The next day in Los Angeles County, he allegedly shot and killed two people, including an off-duty sheriff’s deputy, in apparent random attacks. Following Rhett McKenzie Nelson’s arrest on suspicion of those crimes, the district attorneys in both counties agreed Los Angeles prosecutors would handle the San Diego robbery charges in addition to the murder cases. But this week, San Diego County District Attorney Summer Stephan and one...