RAPID CITY, S.D. – 30-year-old Walter Mousseau Jr. was sentenced today to life in prison for second-degree murder in the death of 43-year-old Sheldon Glenn. Under South Dakota law, a life sentence is mandatory upon conviction for second-degree murder.

The conviction stems from a July 4, 2022, incident in which Mousseau drowned Glenn in the Memorial Park pond in broad daylight, as community members gathered nearby for Independence Day celebrations and a concert at the Memorial Park bandshell.

Assistant Chief Deputy State’s Attorney Jason Thomas told the Court that although today’s sentencing outcome was required by law, the sentencing hearing itself remains an important and necessary part of the process, particularly for those who loved the victim. “This case is about the value of a human life, Sheldon Glenn’s life. Sheldon was a person, not a name in a case file. He had relationships, history, and a future that existed until the moment the defendant decided it no longer did. That opportunity was taken away when the defendant chose to escalate a minor conflict into deadly violence. What was lost that day cannot be restored, and it will never be replaced.”

In addition to the standard guilt phase of the trial, this case included a second phase to address Mousseau’s plea of guilty by reason of insanity. During that phase, the same jury was tasked with determining whether Mousseau was legally insane at the time of the offense. Unlike a traditional criminal trial, the burden in an insanity phase rests with the defense, which must prove by clear and convincing evidence that the defendant was incapable of knowing right from wrong at the time the crime was committed.

The State argued that while Mousseau suffered from mental illness, the evidence did not meet South Dakota’s legal standard for insanity. Prosecutors pointed to Mousseau’s own statements to investigators and bystanders, which demonstrated awareness and intent, as well as toxicology results showing methamphetamine in his system at the time of the killing. Under South Dakota law, drug-induced impairment cannot serve as the basis for an insanity defense.

The jury ultimately found Mousseau was not insane at the time of the offense and returned verdicts of guilty and guilty but mentally ill.

This case was prosecuted by Assistant Chief Deputy State’s Attorney Jason Thomas, Senior Deputy State’s Attorney Braedon Houdek, Deputy State’s Attorney Emily Toms, and Chief Deputy State’s Attorney Gina Nelson.