What is the test for a jury to convict a defendant of involuntary manslaughter?

As the plurality concludes, it was error for the trial court to fail to instruct on the misdemeanor theory of involuntary manslaughter. A trial court must instruct, "sua sponte, on all theories of a lesser included offense which find substantial support in the evidence." (People v. Breverman, supra, 19 Cal.4th 142, 162, 77 Cal.Rptr.2d 870, 960 P.2d 1094.) Here, there was sufficient evidence from which the jury could have convicted defendant of involuntary manslaughter on a misdemeanor theory. Specifically, the jury could have reasonably concluded that when defendant shot and killed his wife he was committing the misdemeanor of brandishing a firearm (Pen.Code, 417, subd. (a)(2)) under circumstances dangerous to human life.

This court has recently held that when a trial court erroneously fails to instruct on a lesser included offense the conviction must be reversed if there is a reasonable probability that the jury could have reached a different conclusion had it been properly instructed. (People v. Breverman, supra, 19 Cal.4th 142, 178, 77 Cal.Rptr.2d 870, 960 P.2d 1094.) Here, there is such a probability. Defendant was highly intoxicated and arguing with his wife when he shot her; there was no direct evidence that he intended to kill her or even that he intended to fire the gun. The jury spent three days deliberating over defendant's level of culpability for causing his wife's death. Having rejected murder, the jury's choice was between voluntary and involuntary manslaughter. Under the instructions given, however, the jury could reach a verdict of involuntary manslaughter only if it found that the killing occurred "[i]n the commission of an act ordinarily lawful, which involves a high degree of risk of death or great bodily harm, without due caution and circumspection." (Italics added.) The jury rejected the view that defendant's acts were merely lawful but dangerous ones in rejecting this theory of involuntary manslaughter.

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