Wisconsin Statutes

Wis. Stat. § 971.15 (2026)

Mental responsibility of defendant

✓ current as of July 2026

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971.15971.15 Mental responsibility of defendant.

971.15(1)(1) A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect the person lacked substantial capacity either to appreciate the wrongfulness of his or her conduct or conform his or her conduct to the requirements of law.

971.15(2)(2) As used in this chapter, the terms “mental disease or defect” do not include an abnormality manifested only by repeated criminal or otherwise antisocial conduct.

971.15(3)(3) Mental disease or defect excluding responsibility is an affirmative defense which the defendant must establish to a reasonable certainty by the greater weight of the credible evidence.

971.15 HistoryHistory: 1993 a. 486.

971.15 AnnotationIt is not a violation of due process to put the burden of the affirmative defense of mental disease or defect on the defendant. State v. Hebard, 50 Wis. 2d 408, 184 N.W.2d 156 (1971).

971.15 AnnotationPsychomotor epilepsy may be legally classified as a mental disease or defect. Sprague v. State, 52 Wis. 2d 89, 187 N.W.2d 784 (1971).

971.15 AnnotationThe state does not have to produce evidence contradicting an insanity defense. The burden is on the defendant. Gibson v. State, 55 Wis. 2d 110, 197 N.W.2d 813 (1972).

971.15 AnnotationA voluntarily drugged condition is not a form of insanity that can constitute a mental defect or disease. Medical testimony cannot be used both on the issue of guilt to prove lack of intent and also to prove insanity. Gibson v. State, 55 Wis. 2d 110, 197 N.W.2d 813 (1972).

971.15 AnnotationThe legislature, in enacting the American Law Institute definition of insanity as this section, deliberately and positively excluded “antisocial conduct” from the statutory definition of “mental disease or defect.” Simpson v. State, 62 Wis. 2d 605, 215 N.W.2d 435 (1974).

971.15 AnnotationThe jury was not obliged to accept the testimony of two medical witnesses, although the state did not present medical testimony, because it was the jury’s responsibility to determine the weight and credibility of the medical testimony. Pautz v. State, 64 Wis. 2d 469, 219 N.W.2d 327 (1974).

971.15 AnnotationThe court properly directed the verdict against the defendant on the issue of mental disease or defect. State v. Leach, 124 Wis. 2d 648, 370 N.W.2d 240 (1985).

971.15 AnnotationDiscussing use of expert evidence of personality dysfunction in the guilt phase of a criminal trial. State v. Morgan, 195 Wis. 2d 388, 536 N.W.2d 425 (Ct. App. 1995), 93-2611.

971.15 AnnotationWhen a defendant requests an 11th-hour change to a not guilty by reason of mental disease or defect plea, the defendant has the burden of showing why the change is appropriate. There must be an offer of proof encompassing the elements of the defense and a showing of why the plea was not entered earlier. State v. Oswald, 2000 WI App 3, 232 Wis. 2d 103, 606 N.W.2d 238, 97-1219.

971.15 AnnotationA court is not required to conduct an on-the-record colloquy with respect to a defendant’s desire to abandon a not guilty by reason of mental disease or defect plea. Only fundamental constitutional rights warrant this special protection, and such a plea falls outside the realm of fundamental rights. State v. Francis, 2005 WI App 161, 285 Wis. 2d 451, 701 N.W.2d 632, 04-1360.

971.15 AnnotationA court is not required to inform a defendant during a plea colloquy that the defendant may plead guilty to a crime and still have a jury trial on the issue of mental responsibility. Because neither the federal or state constitutions confers a right to an insanity defense, a court has no obligation to personally address a defendant in regard to the withdrawal of a not guilty by reason of mental disease or defect plea, although it is the better practice to do so. State v. Burton, 2013 WI 61, 349 Wis. 2d 1, 832 N.W.2d 611, 11-0450.

971.15 AnnotationAlthough expert testimony may be helpful to a defendant in the responsibility phase of the trial, a favorable expert opinion is not an indispensable prerequisite to a finding of mental disease or defect. Although expert testimony is not required, it is highly unlikely that a defendant’s own testimony, standing alone, will be sufficient to satisfy the burden of proof. State v. Magett, 2014 WI 67, 355 Wis. 2d 617, 850 N.W.2d 42, 10-1639.

971.15 AnnotationBecause every person is competent to be a witness under s. 906.01 and there is no exception in s. 906.01 for defendants who have entered a plea of not guilty by reason of mental disease or defect, a defendant is competent to testify to the defendant’s own mental health at the responsibility phase of a trial. This does not mean, however, that the defendant’s testimony alone is sufficient to raise a question for the jury. State v. Magett, 2014 WI 67, 355 Wis. 2d 617, 850 N.W.2d 42, 10-1639.

971.15 AnnotationConsumption of prescription medication cannot give rise to a mental defect that would sustain an insanity defense. Furthermore, it is established law that one who mixes prescription medication with alcohol is responsible for any resulting mental state. State v. Anderson, 2014 WI 93, 357 Wis. 2d 337, 851 N.W.2d 760, 11-1467.

971.15 AnnotationAlthough a better practice, a circuit court is not required to conduct a right-to-testify colloquy at the responsibility phase of a bifurcated trial resulting from a plea of not guilty by reason of mental disease or defect. State v. Lagrone, 2016 WI 26, 368 Wis. 2d 1, 878 N.W.2d 636, 13-1424.

971.15 AnnotationThe Power of the Psychiatric Excuse. Halleck. 53 MLR 229 (1970).

971.15 AnnotationThe Insanity Defense: Conceptual Confusion and the Erosion of Fairness. MacBain. 67 MLR 1 (1983).

971.15 AnnotationCriminal Law—First Degree Murder—Evidence of Diminished Capacity Inadmissible to Show Lack of Intent. Gertig. 1976 WLR 623.

Notes of Decisions

Cited in 93 cases (15 in the last 5 years), 1972–2026 · leading case: State v. Donyil L. Anderson, Sr., 2014 WI 93 (Wis. 2014).

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State v. Donyil L. Anderson, Sr., 2014 WI 93 (Wis. 2014). · cites it 47× “6 Anderson argued that he was not guilty by reason of insanity due to a mental disease or defect under Wis. Stat. § 971.15 . During the insanity phase of the trial, Anderson called an expert witness, Dr.”

State v. James Elvin Lagrone, 2016 WI 26 (Wis. 2016). · cites it 30× “See Wis. Stat. § 971.15 (3). The burden on the defendant is not "beyond a reasonable doubt," but instead "to a reasonable certainty by the greater weight of the credible evidence.”

State v. Corey R. Kucharski, 2015 WI 64 (Wis. 2015). · cites it 17× “" Wis. Stat. § 971.15 (1). The responsibility phase described above has evolved over time and has now become close to a civil trial.”

State v. Erick O. Magett, 2014 WI 67 (Wis. 2014). · cites it 13× “¶33 This case relates to the bifurcated trial described in Wis. Stat. §§ 971.15 and 971.165. A bifurcated criminal trial consists of two phases: (1) the guilt phase; and (2) the responsibility phase.”

State v. Anthony R. Pico, 914 N.W.2d 95 (Wis. 2018). · cites it 4× “" Wis. Stat. § 971.15 (1). 5 No. 2015AP1799-CR ¶8 Mr.”

State v. Randall, 532 N.W.2d 94 (Wis. 1995). · cites it 10× “The standard for finding mental disease or defect as set forth in sec. 971.15(1), Stats., provides: *810 A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacked substantial capacity either to appreciate…”

State v. Corey R. Fugere, 924 N.W.2d 469 (Wis. 2019). · cites it 7× “See Wis. Stat. § 971.15 (1). ¶44 Fourth, NGI commitments do not serve the "traditional aims of punishment——retribution and deterrence.”

State v. Wood, 2010 WI 17 (Wis. 2010). · cites it 4× “See Wis. Stat. § 971.15 (l)(d) (no culpability for criminal conduct where a mental disease causes the person to lack "substantial capacity either to appreciate the wrongfulness of his or her conduct or conform his or her conduct to the requirements of law"); § 971.”

State v. Christopher W. Yakich, 2022 WI 8 (Wis. 2022). · cites it 5× “17 (2017- 18)3 provides circuit courts with the statutory authority to impose consecutive periods of NGI commitment. Because the circuit court properly exercised its authority to impose consecutive NGI 2 In Wisconsin, individuals can be found "not guilty by reason of mental…”

State v. Koput, 418 N.W.2d 804 (Wis. 1988). · cites it 7× “, that if ten of the twelve jurors concluded that Koput suffered from a mental *384 disease and as the result of that disease was not "responsible,” as defined in sec. 971.15, Stats., he was to be exonerated from criminal responsibility for his conduct.”

State v. Fosnow, 2001 WI App 2 (Wis. Ct. App. 2000). · cites it 9× “Despite this, "Krieger failed to obtain any diagnosis that his sexual addiction met the standards" for the lack of criminal responsibility under Wis. Stat. § 971.15 . Id. We concluded: Krieger has failed to differentiate the voluminous psychiatric evidence available before…”

State v. Leach, 370 N.W.2d 240 (Wis. 1985). · cites it 6× “'" [3] Sec. 971.15(3), Stats., provides: "(3) Mental disease or defect excluding responsibility is an affirmative defense which the defendant must establish to a reasonable certainty by the greater weight of the credible evidence.”

Show all 93 citing cases →

— Wis. Stat. § 971.15(1) — 34 cases

State v. Randall, 532 N.W.2d 94 (Wis. 1995). “The standard for finding mental disease or defect as set forth in sec. 971.15(1), Stats., provides: *810 A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacked substantial capacity either to appreciate…”

State v. Krieger, 471 N.W.2d 599 (Wis. Ct. App. 1991).

State v. James Elvin Lagrone, 2016 WI 26 (Wis. 2016). “See Wis. Stat. § 971.15 (3). The burden on the defendant is not "beyond a reasonable doubt," but instead "to a reasonable certainty by the greater weight of the credible evidence.”

State v. Seifert, 454 N.W.2d 346 (Wis. 1990).

Storm Ex Rel. Smoler v. Legion Ins., 2003 WI 120 (Wis. 2003).

— Wis. Stat. § 971.15(2) — 3 cases

State v. Werlein, 401 N.W.2d 848 (Wis. Ct. App. 1987).

State v. Stowe, 932 N.W.2d 179 (Wis. Ct. App. 2019).

Stowe, Graham v. Van Rybroek, Gregory (W.D. Wis. 2023).

— Wis. Stat. § 971.15(3) — 16 cases

State v. Leach, 370 N.W.2d 240 (Wis. 1985). “'" [3] Sec. 971.15(3), Stats., provides: "(3) Mental disease or defect excluding responsibility is an affirmative defense which the defendant must establish to a reasonable certainty by the greater weight of the credible evidence.”

State v. Koput, 418 N.W.2d 804 (Wis. 1988). “, that if ten of the twelve jurors concluded that Koput suffered from a mental *384 disease and as the result of that disease was not "responsible,” as defined in sec. 971.15, Stats., he was to be exonerated from criminal responsibility for his conduct.”

State v. Corey R. Kucharski, 2015 WI 64 (Wis. 2015). “" Wis. Stat. § 971.15 (1). The responsibility phase described above has evolved over time and has now become close to a civil trial.”

— Wis. Stat. § 971.15(6)(b) — 1 case

State v. Christopher W. Yakich, 2022 WI 8 (Wis. 2022). “17 (2017- 18)3 provides circuit courts with the statutory authority to impose consecutive periods of NGI commitment. Because the circuit court properly exercised its authority to impose consecutive NGI 2 In Wisconsin, individuals can be found "not guilty by reason of mental…”

— Wis. Stat. § 971.15(8) — 1 case

State v. Smith, 344 N.W.2d 711 (Wis. Ct. App. 1983).

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