RAPID CITY, SD — In a solemn judgment rendered at the close of 2025, a South Dakota man was sentenced to life imprisonment without the possibility of parole for the drowning death of another man during a Fourth of July celebration. Walter Mousseau Jr., 30, was found guilty but mentally ill of second-degree murder after a tragic incident at Memorial Park in Rapid City that left the community in shock.
The sentence followed a guilty verdict in the 2022 death of 43-year-old Sheldon Glenn, where onlookers witnessed the horrific scene of Mousseau holding Glenn underwater despite desperate pleas to relent. This incident not only disturbed the festive atmosphere but also prompted a rigorous legal examination of mental illness in criminal justice.
During Mousseau’s trial, the defense argued that his schizophrenia diagnosis and history of substance abuse should exempt him from criminal responsibility. However, despite expert testimony regarding Mousseau’s delusional state and irrational beliefs — including his claim of “eyes in the sky” watching him — jurors concluded that he was sufficiently aware of his actions at the time of the killing.
The court heard from mental health professionals and eyewitnesses, whose combined testimonies painted a complex picture of Mousseau’s psychological condition. Nevertheless, the jury ultimately rejected the insanity defense, influenced by evidence that suggested Mousseau had previously entertained thoughts of violence under certain circumstances.
Judicial proceedings were notably extended due to comprehensive mental fitness evaluations, reflecting the complexities involved when legal and psychological assessments intersect. The prosecution, on the other hand, maintained that the murder was a calculated act, underscoring the permanence of the loss inflicted on Glenn’s family. They portrayed the drowning as a conscious and deliberate escalation of violence by Mousseau.
Judge Eric Kelderman of Pennington County’s 7th Judicial Circuit Court delivered the life sentence, marking a decisive end to a case that deeply affected both the victim’s relatives and bystanders who witnessed the crime. The prosecution emphasized the depth of sorrow experienced by Glenn’s loved ones, stating that the victim was far more than just a figure in court documents but a significant life cut tragically short.
This case has reignited discussions on mental health’s role in criminal proceedings, specifically regarding the degree to which mental illness can or should influence accountability in severe criminal acts. The court’s decision underscores a prevailing judicial perspective that mental health issues, while pivotal for understanding behavior, do not absolve individuals from the consequences of violent crimes.
As Mousseau begins his life sentence, the repercussions of this tragic event continue to ripple through the Rapid City community, especially poignant during a time typically associated with national celebration and community. The state’s firm response to this violent act underlines its commitment to holding individuals accountable, regardless of their mental health background.
Authorities reiterated that despite the considerations of Mousseau’s mental health, the severity of the offense and its devastating impact leaves no room for leniency. This stance reflects a broader consensus on the delicate balance between acknowledging mental illness and ensuring justice for violent crimes.
The relentless unfolding of this case and its ultimate conclusion remains a stark reminder of the crucial intersections between mental health awareness and criminal accountability. As Glenn’s family and the community at large grapple with the aftermath, this case serves as a sobering testament to the complexities facing modern jurisprudence.