(a) The grand jury may inquire into all public offenses committed or triable within the county and present them to the court by indictment.
(b) Except as provided in Section 918, the grand jury shall not inquire into an offense that involves a shooting or use of excessive force by a peace officer described in Section 830.1, subdivision (a) of Section 830.2, or Section 830.39, that led to the death of a person being detained or arrested by the peace officer pursuant to Section 836.