The district courts are hereby vested with power to call grand juries. It shall be mandatory for such district courts to call a grand jury in each case upon the petition of the registered voters of the county of the number of not less than ten percent of the total vote cast for the office of Governor in such county at the most recent general election held for such office. A grand jury may be called and summoned in the manner provided by law on such day of a regular term of the district court in each year in each county of the state as the district court may direct and at such other times and upon such notice as the district court may deem necessary. District courts shall call a grand jury in each case upon certification by the county coroner or coroner's physician that an individual has died while being apprehended by or while in the custody of a law enforcement officer or detention personnel. Any grand jury called pursuant to this section shall be limited in its charge, powers, duties, proceedings, indictment, and report to the review of the incident or incidents which caused it to be called.