(a) Upon a trial for murder, the commission of the homicide by the defendant being proved, the burden of proving circumstances of mitigation, or that justify or excuse it, devolves upon the defendant, unless the proof on the part of the prosecution tends to show that the crime committed only amounts to manslaughter, or that the defendant was justifiable or excusable.
(b) Nothing in this section shall apply to or affect any proceeding under Section 190.3 or 190.4.
(Added by Stats. 1989, Ch. 897, Sec. 16.)