Background
Katherine Anne Proctor, then an Assistant Montana Attorney General, was convicted of felony Assault on a Minor after her four-month-old daughter P.P. arrived at a Helena emergency room on September 29, 2021, in critical condition. Medical personnel found P.P. unresponsive, seizing, and suffering from a massive anoxic brain injury, subdural hemorrhages, retinal hemorrhages, cervical ligamentous injury, multiple rib fractures in various stages of healing, and a femur fracture. Treating physicians in Helena and Kalispell each independently concluded the constellation of injuries was consistent with non-accidental trauma (NAT) — also called Abusive Head Trauma (AHT) or, colloquially, Shaken Baby Syndrome (SBS). P.P. survived but was left with irreversible, catastrophic brain damage requiring full-time care for the rest of her life.
Investigators from the Lewis & Clark County Sheriff’s Office obtained a search warrant for Proctor’s and her husband’s smartphones, extracting all stored data (subject to limited exceptions for attorney-client and clergy communications). The State charged Proctor with one count of Assault on a Minor under § 45-5-212, MCA, alleging that she had inflicted recurring abuse over a period spanning June through October 2021. Tim Proctor, P.P.’s father, was not charged; medical evidence indicated the most acute brain injury occurred during a narrow window on the evening of September 28, 2021, when Proctor was alone with P.P.
Before trial, Proctor moved to exclude all SBS/AHT expert testimony as scientifically unreliable and to suppress the smartphone evidence as the product of an unconstitutionally overbroad general warrant. Both motions were denied by the First Judicial District Court. After a December 2022 jury trial featuring dueling expert witnesses, the jury returned a guilty verdict. Proctor was sentenced to 20 years in the Montana Women’s Prison and appealed on four grounds: admission of SBS expert testimony, the cell-phone warrant, prosecutorial misconduct in closing argument, and ineffective assistance of counsel.
The Court’s Holding
The Montana Supreme Court affirmed the conviction on all four issues. On the central question of SBS/AHT expert testimony, the court rejected Proctor’s reliance on State v. Nieves, in which New Jersey courts excluded SBS/AHT evidence because it failed the Frye “general acceptance” standard across all relevant scientific disciplines, including biomechanics. The Montana court noted that Montana abandoned the Frye general-acceptance test more than four decades ago in Barmeyer v. Montana Power Co., 202 Mont. 185 (1983), because it no longer conformed with Montana’s rules of evidence. Under Montana’s approach, absolute certainty or scientific unanimity is not required for admissibility; conflicts among experts go to the weight of evidence, not its threshold admissibility. Critically, the prosecution’s case did not rest solely on the disputed classical SBS triad (subdural hemorrhage, retinal hemorrhage, encephalopathy), but on a broader NAT diagnosis supported by additional injuries — rib fractures, femur fracture, cervical ligamentous injury, and brain contusion — that the State’s experts diagnosed through a reliable differential-diagnosis methodology accepted by the major medical associations.
On the warrant issue, the court upheld the District Court’s denial of suppression, crediting the finding that the warrant’s scope was tied to evidence related to the Owlet infant monitor application, photographs of P.P., and messages referencing P.P. or her injuries, and that temporal limitations provided the requisite specificity. On prosecutorial misconduct, the court reviewed under the plain-error doctrine because Proctor failed to object at trial, and found no basis for reversal. The claim of ineffective assistance of counsel likewise failed under de novo review.
Key Takeaways
- Montana does not apply the Frye general-acceptance test, so SBS/AHT expert testimony is not categorically excludable merely because biomechanical researchers dispute the pure non-impact shaking hypothesis — the relevant question is reliability of the diagnostic methodology under Montana’s rules of evidence.
- A NAT/AHT diagnosis supported by a differential-diagnosis process that rules out infection, bleeding disorders, and other organic causes, and that encompasses injuries beyond the classical triad (such as rib fractures, femur fractures, and cervical ligamentous injury), is admissible in Montana even where competing experts challenge individual findings.
- A cell-phone warrant seeking “all data currently stored” on a device is not automatically an unconstitutional general warrant where the affidavit ties the device to the crime (here, the Owlet monitor app) and where the data actually extracted is limited to evidence relevant to the charged conduct.
- Failure to contemporaneously object to prosecutorial closing argument confines appellate review to the narrow plain-error doctrine; character-based rhetorical flourishes in closing do not automatically warrant a new trial absent a showing of manifest injustice.
Why It Matters
State v. Proctor is a significant data point in the ongoing national debate over SBS/AHT prosecutions. New Jersey’s Nieves decisions, issued in 2023 and 2025, raised the prospect that Frye-jurisdiction courts might systematically exclude SBS/AHT evidence absent cross-disciplinary validation. Montana’s opinion illustrates the opposite trajectory in Daubert-lineage jurisdictions that have abandoned Frye: courts in those states will assess whether the diagnostic methodology — differential diagnosis, integration of clinical findings, imaging, and laboratory results — is reliable, rather than demanding consensus across every underlying scientific field. Defense practitioners in child-abuse cases will need to tailor their Daubert challenges to the specific methodology and the full injury picture, not merely to biomechanical disputes about non-impact shaking.
The decision also reinforces that smartphone search warrants tied to specific investigative leads (here, a companion app for an infant monitor) can withstand overbreadth challenges even when the warrant authorizes extraction of broad categories of device data, so long as actual production is bounded by relevance to the charged conduct. Prosecutors and investigators seeking comprehensive device extractions should document the nexus between the specific app or device function and the alleged crime in their warrant affidavits.