Generally, appellate courts cannot consider trial testimony in reviewing a decision denying a pretrial motion (People v Gonzalez, 55 NY2d 720 [1981]). An important exception to this rule is that appellate courts can look at the trial evidence in determining whether a motion for severance should have been granted (People v Lopez, 68 NY2d 683 [1986])

A recent example of how trial evidence can be considered by an appellate court reviewing the denial of a pre-trial motion for severance, is the decision of the Appellate Division, Fourth Department in People v Nixon (2010 NY Slip Op 06997 [4th Dept 10/01/2010]), in which the Court wrote

In support of his pretrial motion for severance, defendant contended that he and the codefendant had irreconcilable defenses because, according to defendant, the codefendant was in sole possession of the weapon, while the defense of the codefendant was that defendant possessed the weapon but placed it under the codefendant's passenger seat when the police stopped the vehicle. Defendant further contended that he would be prejudiced in the event that the codefendant's attorney was permitted to present evidence against him, thereby acting as a second prosecutor. Indeed, defendant was correct in that respect because the codefendant's "attorney took an aggressive adversarial stance against [defendant at trial], in effect becoming a second prosecutor" (People v Cardwell, 78 NY2d 996, 998). In support of his motion for a mistrial following the testimony of the codefendant at trial, defendant contended that the codefendant had testified that defendant stated that he could not be caught with a handgun because he was on parole, and we note in any event that both defendants in fact implicated each other at trial (cf. People v Watkins, 10 AD3d 665, 665-666, lv denied 3 NY3d 761). Consequently, we agree with defendant that " [t]he essence or core of the [*2]defenses [were] in conflict, such that the jury, in order to believe the core of one defense, must necessarily disbelieve the core of the other' " (People v Mahboubian, 74 NY2d 174, 184). In view thereof, along with the fact that "there [was] a significant danger, as both defenses [were] portrayed to the trial court [in the pretrial motion and the motion for a mistrial], that the conflict alone would lead the jury to infer defendant's guilt," severance was required (id.; see People v Kyser, 26 AD3d 839, 840). Although it appears from the record that the court did not address defendant's irreconcilable conflict contention in refusing to sever the trial or to grant a mistrial, that failure is of no moment because we deem the court to have implicitly denied the severance and mistrial motions on that ground (see generally People v Mason, 305 AD2d 979, lv denied 100 NY2d 563). Consequently, we reverse the judgment and grant a new trial. Inasmuch as the codefendant was acquitted at trial, defendant's severance motion is moot.