State v. Montgomery, 536 P.3d 627

Defendant was convicted after a jury trial of first‑degree sodomy based on allegations that he entered KC’s bedroom while she slept and performed oral sex on her.
Defendant admitted to police that he had oral sex with KC but claimed he believed it was consensual; at trial he said he had lied initially to protect KC.
Before trial, defendant sought to testify that KC had an extramarital affair about five years earlier (which led to a divorce and later reconciliation) to show motive to fabricate; the trial court excluded that testimony.
During closing argument and rebuttal, the prosecutor repeatedly told the jury that defendant was a liar and that he would not tell the truth; defense counsel did not object at trial.
On appeal the court found the prosecutor’s repeated statements constituted improper vouching so prejudicial that, under plain‑error review, reversal and remand were required; the court also held the trial court did not err in excluding the prior‑sexual‑behavior evidence under OEC 412.

Issue	State's Argument	Montgomery's Argument	Held
Whether the prosecutor’s repeated statements that defendant lied constituted improper vouching and, if unpreserved, plain error	The prosecutor’s comments were fair argument about credibility and did not misstate the burden of proof	The comments were improper vouching (“take my word for it”) that deprived defendant of a fair trial; plain error review applies	The statements were improper vouching and, considered in context, so prejudicial that they met the Chitwood plain‑error standard; conviction reversed and remanded
Whether the trial court erred in excluding evidence of KC’s prior extramarital affair (evidence of past sexual behavior/motive to fabricate)	The evidence was irrelevant to motive and properly excluded under OEC 412’s protective rules	The past affair tended to show a motive to fabricate to avoid upsetting KC’s spouse	The exclusion was not error: the prior affair did not make fabrication more or less probable and was the sort of collateral sexual‑history evidence OEC 412 prohibits

State v. Chitwood, 370 Or 305 (2022) (plain‑error framework for unpreserved prosecutorial misconduct; legal error requires prejudice so great an instruction would not cure)
State v. Pierpoint, 325 Or App 298 (applying Chitwood to determine whether prosecutorial comments were incurable)
State v. Sperou, 365 Or 121 (2019) (prosecutor may not express personal opinion on witness credibility)
State v. Rosasco, 103 Or 343 (state’s burden is proof beyond a reasonable doubt)
State v. Brown, 306 Or 599 (jury’s function to weigh evidence and judge witness credibility)