State v. Nichols, 339 P.3d 1274

In early 2010 Thomas Nichols lived briefly with girlfriend Kay Lynn and her family, including 9‑year‑old T.K.; T.K. later accused Nichols of touching her crotch while they watched a movie.
T.K. gave a forensic interview and testified at trial; a sexual assault nurse examiner found a normal exam.
Nichols was charged with Sexual Assault and Sexual Intercourse Without Consent; a jury convicted him on both counts in November 2011.
At trial the State elicited testimony about Nichols’ private sexual practices and details of his sex life with Kay Lynn from multiple witnesses.
Detective Buls, the primary investigator, was designated as the State’s representative and remained in the courtroom and testified.
Nichols appealed, arguing (inter alia) that the admission of sexual‑habits evidence and allowing the investigator to serve as both State representative and witness were erroneous; the Court reversed and remanded.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Admissibility of testimony about defendant's sexual habits	State: Defense opened door by describing Nichols’ “healthy, active sex life,” and testimony was relevant to witness bias and impeachment	Nichols: Evidence was irrelevant and unduly prejudicial; should be excluded under M. R. Evid. 403	Court: Admission of inflammatory, detailed sexual‑practice testimony was an abuse of discretion and likely contributed to the conviction; reversal required
Use of investigator as State representative while testifying (Rule 615)	State: Faulconbridge permits a designated representative to remain and testify; applies to criminal cases	Nichols: Faulconbridge was a civil case and should not control criminal proceedings	Court: Faulconbridge applies; a validly designated representative may remain and testify (court commented on this issue while reversing on other grounds)

Seltzer v. Morton, 154 P.3d 561 (Mont. 2007) (district court has broad discretion over evidentiary rulings)
State v. Derbyshire, 201 P.3d 811 (Mont. 2009) (de novo review for interpretations of evidentiary rules)
State v. Gray, 673 P.2d 1262 (Mont. 1983) (reversal required if inadmissible evidence might have contributed to conviction)
State v. Van Kirk, 32 P.3d 735 (Mont. 2001) (two‑step prejudice analysis distinguishing structural and trial error)
Faulconbridge v. State, 142 P.3d 777 (Mont. 2006) (designated party representative may remain in courtroom and testify under Rule 615)
K & R P’ship v. City of Whitefish, 189 P.3d 593 (Mont. 2008) (appellate courts may address additional issues to provide guidance on remand)