What is the burden of proving a defendant guilty of a charge of murder?

Four criteria used to determine whether the defendant has met his burden "are these: (1) would the evidence of the crimes be cross-admissible in separate trials; (2) are some of the charges unusually likely to inflame the jury against the defendant; (3) has a weak case been joined with a strong case or another weak case so that the total evidence on the joined charges may alter the outcome of some or all of the charged offenses; and (4) is any one of the charges a death penalty offense, or does joinder of the charges convert the matter into a capital case. [Citation.]" (People v. Marshall, supra, 15 Cal.4th at pp. 27-28.)