not include McCormick as an aggressor, the jury found Defendant guilty of McCormick’s murder. It is not possible to determine whether the jury rendered a proper verdict when the defense instructions were inadequate regarding the shooting of McCormick. Accordingly, we have grave concerns about whether the jury understood Defendant’s theory of defense and considered the facts in light of his theory. See State v. Mascareñas, 2000-NMSC-017, ¶ 21, 129 N.M. 230, 4 P.3d 1221 (reversing the defendant’s conviction under the fundamental error rule because there was “simply no way to determine that the jury delivered its verdict on a legally adequate basis”); cf. Cunningham, 2000-NMSC-009, ¶¶ 15-19, 128 N.M. 711, 998 P.2d 176 (declining to invoke the fundamental error rule beca . 692, 42 P.3d 272 (<HOLDING>). Because the error went to the heart of
holding that the improper use of a mixedmotive instruction in a butfor case shifted the burden of persuasion on a central issue in the case and therefore the error cannot be harmless holding that it was not error for the court to give a substantive new instruction to the jury after deliberations began where the instruction was given in court with the defendant and his counsel present recognizing that in any criminal trial the credibility of the prosecutions witnesses is central holding that in a criminal trial the trial court must correct or amend an improper instruction if the proper instruction is necessary for the jury to understand the case recognizing that in such close circumstances where the error involves the central issue in the case it is the better policy to require a new trial under the correct instruction