138 F.4th 1274
10th Cir.2025Background
- Perry Maryboy was convicted of second-degree murder after shooting Antonio Montowine during a roadside encounter near Bluff, Utah.
- Competing trial narratives were presented: Maryboy claimed the shot was accidental during a warning shot fired out of self-defense; the government alleged an intentional or extremely reckless killing.
- The key disputed issue at trial was whether Maryboy acted with malice aforethought (required for 2nd degree murder) or was merely reckless (which would support involuntary manslaughter).
- At trial, both perfect and imperfect self-defense theories were put forward, with only perfect self-defense (objectively reasonable fear) being a complete defense.
- The jury instructions included perfect self-defense but erroneously limited the instruction on imperfect self-defense to involuntary manslaughter.
- Maryboy appealed, arguing (1) the government’s expert improperly testified about his mental state, and (2) the jury was improperly instructed on the government's burden regarding imperfect self-defense.
Issues
| Issue | Plaintiff's Argument | Defendant's Argument | Held |
|---|---|---|---|
| Improper Expert Testimony under Rule 704(b) | Govt expert’s testimony that conduct was “extreme recklessness” opined on Maryboy’s mental state (mens rea), a jury issue. | Olson’s testimony addressed gun safety rules/was about conduct, not state of mind. | Testimony violated Rule 704(b); error was plain and prejudiced Maryboy. |
| Faulty Jury Instructions (Imperfect Self-Defense) | Jury not told govt had to disprove imperfect self-defense for 2nd-degree murder beyond a reasonable doubt. | Govt had no duty to give instruction absent sufficient trial evidence; any error not prejudicial. | Instruction error violated due process; was plain and prejudiced Maryboy. |
| Prejudice to Substantial Rights | Errors caused possible wrongful conviction of 2nd-degree murder rather than involuntary manslaughter. | Ample evidence of intentional shooting/minor portion of record. | Errors likely affected the outcome; confidence in verdict undermined. |
| Cumulative Error | If not individually, the errors together warrant reversal. | Evidence of intent too strong/cumulative error principle not applicable. | Cumulative error warrants reversal and new trial. |
Key Cases Cited
- United States v. Wood, 207 F.3d 1222 (10th Cir. 2000) (expert testimony tracking mens rea language violates Rule 704(b))
- Diaz v. United States, 602 U.S. 526 (2024) (expert cannot opine directly on defendant’s mental state, but general group opinions do not violate 704(b))
- United States v. Lofton, 776 F.2d 918 (10th Cir. 1985) (absence of instruction on government’s burden to disprove mitigating defense is plain error)