A motion to sever is to have the judge order a separate trial for each co-defendant.

California Penal Code section 1098 states as follows:

“When two or more defendants are jointly charged with any public offense, whether felony or misdemeanor, they must be tried jointly, unless the court order[s] separate trials. In ordering separate trials, the court in its discretion may order a separate trial as to one or more defendants, and a joint trial as to the others, or may order any number of the defendants to be tried at one trial, and any number of the others at different trials, or may order a separate trial for each defendant; provided, that where two or more persons can be jointly tried, the fact that separate accusatory pleadings were filed shall not prevent their joint trial.”

(Pen. Code, § 1098 [brackets added as sic in original].)

“Penal Code section 1098 in 1921 abrogated the former rule that codefendants enjoyed an absolute right to separate trials, restoring the common law rule which placed the matter within the discretion of the trial court. (See United States v. Marchant (1827) 25 U.S. (12 Wheat.) 480, 481-484 [6 L.Ed. 700]; Witkin, Cal. Criminal Procedure (1963) § 291; and cases there cited.) Older cases had held almost unanimously that a court could never abuse its discretion in denying a motion for a separate trial because the jury could be admonished not to consider prejudicial testimony admissible only against a codefendant.  The more recent cases, however, recognizing the impossibility of a juror’s obliteration from his mind of that which he already knew, have held that the court should separate the trials of codefendants in the face of an incriminating confession, prejudicial association with codefendants, likely confusion resulting from evidence on multiple counts, conflicting defenses, or the possibility that at a separate trial a codefendant would give exonerating testimony.

(People v. Massie (1967) 66 Cal.2d 899, 916-917 [59 Cal.Rptr. 733, 428 P.2d 869] [bold added].)

“Severance may also be appropriate where ‘ ‘there is a serious risk that a joint trial would compromise a specific trial right of one of the defendants, or prevent the jury from making a reliable judgment about guilt or innocence.’ ’ (People v. Lewis (2008) 43 Cal.4th 415, 452 [75 Cal. Rptr. 3d 588, 181 P.3d 947], quoting Zafiro v. United States (1993) 506 U.S. 534, 539 [122 L. Ed. 2d 317, 113 S. Ct. 933].) ‘If we conclude the trial court abused its discretion, reversal is required only if it is reasonably probable the defendant would have obtained a more favorable result at a separate trial.’ (People v. Burney (2009) 47 Cal.4th 203, 237 [97 Cal. Rptr. 3d 348, 212 P.3d 639].) But, ‘[e]ven if a trial court’s severance or joinder ruling is correct at the time it was made, a reviewing court must reverse the judgment if the ‘defendant shows that joinder actually resulted in ‘gross unfairness’ amounting to a denial of due process.’’ (People v. Mendoza (2000) 24 Cal.4th 130, 162 [99 Cal. Rptr. 2d 485, 6 P.3d 150], quoting People v. Arias (1996) 13 Cal.4th 92, 127 [51 Cal. Rptr. 2d 770, 913 P.2d 980].)”

(People v. Gomez (2018) 6 Cal.5th 243, 274 [240 Cal.Rptr.3d 315, 430 P.3d 791] [bold added].)

“In conclusion, where two dissimilar offenses occur a significant period of time apart, are connected only by an otherwise unidentified weapon, and proof of one charge involves potentially prejudicial and otherwise inadmissible evidence on the second charge, the refusal to grant a motion to sever the charges is an abuse of discretion.” (Walker v. Superior Court (1974) 37 Cal.App.3d 938, 943 [112 Cal.Rptr. 767].)

In People v. Bradford (1997) 15 Cal.4th 1229, the Supreme Court of California endeavored to identify factors that would cause a reviewing court to decide a trial court abused its discretion in failing to sever:

“‘ ‘The burden is on the party seeking severance to clearly establish that there is a substantial danger of prejudice requiring that the charges be separately tried.’ [Citation.] ‘The determination of prejudice is necessarily dependent on the particular circumstances of each individual case, but certain criteria have emerged to provide guidance in ruling upon and reviewing a motion to sever trial.’ [Citation.] Refusal to sever may be an abuse of discretion where: (1) evidence on the crimes to be jointly tried would not be cross-admissible in separate trials; (2) certain of the charges are unusually likely to inflame the jury against the defendant; (3) a ‘weak’ case has been joined with  a ‘strong’ case, or with another ‘weak’ case, so that the ‘spillover’ effect of aggregate evidence on several charges might well alter the outcome of some or all of the charges; and (4) any one of the charges carries the death penalty or joinder of them turns the matter into a capital case. [Citations.]’ ( People v. Sandovalsupra, 4 Cal. 4th 155, 172-173; People v. Mayfieldsupra, 14 Cal. 4th 668, 721; People v. Memro (1995) 11 Cal. 4th 786, 849-850 [47 Cal. Rptr. 2d 219, 905 P.2d 1305]; People v. Davissupra, 10 Cal. 4th 463, 507-508; People v. Mason (1991) 52 Cal. 3d 909, 933-934 [277 Cal. Rptr. 166, 802 P.2d 950]; Williams v. Superior Court (1984) 36 Cal. 3d 441, 452-454 [204 Cal. Rptr. 700, 683 P.2d 699].)”

(People v. Bradford, supra, 15 Cal.4th at 1315 [65 Cal.Rptr.2d 145, 939 P.2d 259] [bold added].)

In addition, the Supreme Court of California has articulated that due process must be considered both at the time of the motion and in retrospect by the reviewing court:

“We have held that even if a trial court’s ruling on a motion to sever is correct at the time it was made, a reviewing court still must determine whether, in the end, the joinder of counts or defendants for trial resulted in gross unfairness depriving the defendant of due process of law. (People v. Mendoza (2000) 24 Cal.4th 130, 162 [99 Cal. Rptr. 2d 485, 6 P.3d 150]; People v. Ochoa (1998) 19 Cal.4th 353, 409 [79 Cal. Rptr. 2d 408, 966 P.2d 442]; see also People v. Grant (2003) 113 Cal.App.4th 579, 594 [6 Cal. Rptr. 3d 560] [finding gross unfairness even though trial court did not err in ruling on motion for severance].) Defendant asserts such review for gross unfairness is available even when no motion to sever ever was made. (See People v. Simms (1970) 10 Cal. App. 3d 299, 308–309, 317 [89 Cal. Rptr. 1] [reviewing joint trial for gross unfairness, and finding none, even in the absence of a motion to sever defendant’s trial from that of codefendant]; People v. Chambers (1964) 231 Cal. App. 2d 23, 28, 34 [41 Cal. Rptr. 551] [reversing judgment in the absence of an objection to joinder of defendant’s trial with that of codefendant, where joinder in combination with other errors resulted in gross unfairness and denial of due process]; cf. People v. Burns (1969) 270 Cal. App. 2d 238, 251–253 [75 Cal. Rptr. 688] [reviewing for gross unfairness following an untimely motion to sever].)”

(People v. Rogers (2006) 39 Cal.4th 826, 851 [48 Cal.Rptr.3d 1, 141 P.3d 135].)

The California Supreme Court has aided trial courts in promoting a particular sequence when addressing severance factors:

“Our determination whether defendant was prejudiced by joinder requires us first to examine whether evidence on each of the joined charges would have been admissible, under Evidence Code section 1101, in separate trials on the others. If so, any inference of prejudice is dispelled. ( People v. Bradfordsupra, 15 Cal. 4th at pp. 1315-1316.) Conversely, however, the absence of cross-admissibility does not, by itself, demonstrate prejudice. ( Id. at p. 1316.)”

(People v. Kraft (2000) 23 Cal.4th 978, 1030 [99 Cal.Rptr.2d 1, 5 P.3d 68].) However, the Supreme Court of California has noted that identity evidence would almost certainly fail to meet the requisite standards for admission:

“In the present case, one of the crucial issues facing the jury will be the identity of the perpetrator(s) of the two killings and the related crimes. If the trials were to be severed, it is likely that the prosecution would try to introduce evidence relating to one of the shootings at the trial involving the other incident, on the grounds that such evidence would be probative of the identity of the killer. This is the only theory upon which such ‘other crimes’ evidence might be admissible in the instant case, and it would almost certainly fail to meet the requisite standards for admission.”

(Williams v. Superior Court (1984) 36 Cal.3d 441, 449 [204 Cal.Rptr. 700, 683 P.2d 699] disapproved on other grounds as stated in Alcala v. Superior Court (2008) 43 Cal.4th 1205, 1229, fn. 19.)