An attorney for Walter Mousseau has asked for a new trial, arguing prosecutors introduced false evidence during the insanity phase of his 2025 murder trial.
Mousseau, 30, was convicted of second-degree murder—guilty but mentally ill—for the 2022 drowning death of Sheldon Glenn and is serving a mandatory life sentence.
The defense says the trial was unfair because a key mental‑health witness was unexpectedly hospitalized and unable to testify, yet prosecutors referenced statements she never made. The motion also cites concerns about a prospective juror who praised prosecutor Gina Nelson during jury selection and claims a jury instruction on intoxication and insanity was misleading.
The state has not filed a response. If no ruling is issued within 20 business days of the Jan. 26 filing, the request is automatically denied and sent to the South Dakota Supreme Court.
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