Overview

Last seen: May 6, 1979
Location: Her home on Fennimore Lane, Muskego, Waukesha County, Wisconsin
Age: 38
Status: Murder victim; remains have never been recovered
Convicted: Husband John H. Bayerl
Conviction: First-degree murder, June 26, 2019
Sentence: Life imprisonment, August 30, 2019
Key circumstances: Dona disappeared following an argument with her husband. The family vehicle returned to the residence, but Dona vanished. She was not reported missing until May 9. Investigators later relied on circumstantial evidence, witness testimony, John’s statements and preserved blood evidence. Nearly 40 years after the disappearance, John was arrested, prosecuted and convicted. Dona’s remains remain missing.

Detailed Case Breakdown

Dona Mae Bayerl: The 1979 Muskego, Wisconsin Murder and Search for Her Remains

Dona Mae Bourgeois Bayerl was a 38-year-old mother of two when she vanished from Muskego, Wisconsin, on May 6, 1979. For nearly four decades, her disappearance remained one of Wisconsin’s enduring cold cases. Her body has never been recovered, but prosecutors eventually built a circumstantial murder case against her husband, John H. Bayerl, resulting in his conviction for first-degree murder in 2019.

The Night Dona Mae Bayerl Disappeared

Dona Mae was last seen at the family’s home on Fennimore Lane in Muskego on May 6, 1979. John Bayerl told investigators that he and Dona had argued and that she became upset and drove away in the family’s car.

According to the account John provided, he later heard what he believed was Dona returning. The family vehicle was subsequently found back at the residence, but Dona was gone. When the couple’s children awoke the following morning, their mother was not there.

John did not report Dona missing until May 9, three days after she was last seen. Her family and friends disputed the idea that she would voluntarily abandon her children. Dona never contacted her daughters or relatives again, and there was no confirmed evidence that she began a new life elsewhere.

Evidence at the Bayerl Home

Investigators returned to the Bayerl residence as the missing-person investigation developed. According to the criminal-case evidence later described in court records and contemporary reporting, investigators discovered suspected blood in the garage, including staining on objects there.

DNA technology was not available to investigators in 1979 in the way it would become decades later. Evidence preserved from the investigation therefore became significantly more important as forensic technology improved. Testing conducted years later connected blood evidence recovered from the garage to Dona Mae’s DNA profile.

Investigators also learned about problems within Dona and John’s marriage. Evidence presented decades later at trial included John’s admitted physical abuse of Dona and infidelity before her disappearance. Prosecutors also introduced testimony concerning his conduct in later relationships.

A Missing-Person Case Becomes a Homicide Investigation

Dona remained missing year after year. John Bayerl was granted a divorce in 1980, and Dona was legally declared dead in 1986. Her remains, however, were never discovered.

The Muskego Police Department continued investigating the case rather than permanently closing it. John remained a person of interest, and authorities eventually reclassified the disappearance as a homicide investigation.

The case received renewed public attention decades later. Investigators worked with Dona’s family and forensic artists, and an age-progression image was released in an effort to generate new information.

Detective Stephen Westphal, who took over work on the case decades after Dona disappeared, played a major role in the renewed investigation. Evidence accumulated during the original investigation was revisited, witnesses and statements were reconsidered, and old physical evidence could be examined using technology unavailable in 1979.

Arrest Nearly 40 Years Later

A major breakthrough became public in February 2019.

Authorities obtained an arrest warrant for John Bayerl on a charge of first-degree murder. Muskego detectives traveled to Fort Myers, Florida, where Bayerl was living, and worked with Florida authorities to take him into custody. He was returned to Wisconsin to face prosecution for Dona’s death.

It was an unusual murder prosecution because investigators still had not recovered Dona’s body. The state’s case therefore depended heavily on circumstantial evidence, witness testimony, John’s statements over the years, evidence concerning the marriage, and physical evidence preserved from the original investigation.

The 2019 Murder Trial

John Bayerl’s trial took place in Waukesha County in June 2019.

Among the evidence presented to jurors was blood evidence associated with the Bayerl garage. Prosecutors also presented evidence about the deteriorating marriage, John’s admitted mistreatment of Dona, his infidelity, statements he made about Dona’s disappearance, and testimony from women with whom he later had relationships.

The defense emphasized the circumstantial nature of the prosecution’s case and challenged whether the evidence established beyond a reasonable doubt that John intentionally killed Dona. John did not testify at trial.

On June 26, 2019, after approximately five hours of deliberation, the jury found John H. Bayerl guilty of first-degree murder.

Life Sentence — But Dona Was Still Missing

On August 30, 2019, John Bayerl was sentenced to life in prison.

The conviction answered the legal question of responsibility for Dona’s death, but it did not answer the question that remained most important to her family: where was she?

At sentencing, Dona’s daughters appealed for information that could lead them to their mother’s remains and allow them to give her a proper burial. John maintained his innocence and said he did not know what had happened to Dona or where she was.

Consequently, Dona’s case has an unusual status. There is a murder conviction, but the victim’s remains are still missing.

Appeal of John Bayerl’s Murder Conviction

John Bayerl subsequently challenged his conviction.

His appeal argued, among other things, that the trial court improperly admitted certain other-acts evidence and that he had received ineffective assistance from his trial attorney. He also sought a new trial in the interest of justice.

On June 21, 2023, the Wisconsin Court of Appeals rejected those arguments and affirmed the conviction and the order denying postconviction relief.

Wisconsin court records show that a petition for review was subsequently filed with the Wisconsin Supreme Court. The appellate docket records later proceedings through January 2024, including dismissal as moot of a motion seeking additional time to submit a motion for reconsideration.

Latest Publicly Available Investigation Information

Dona Mae’s remains have still not been publicly reported as recovered.

The Wisconsin Department of Justice Clearinghouse for Missing & Exploited Children & Adults continues to maintain an active public page for Dona Mae Bourgeois Bayerl. The state page identifies Muskego as the location from which she disappeared, notes John Bayerl’s 2019 murder conviction, and specifically states that the whereabouts of her remains are still unknown. The agency continues to request information and directs tips to the Muskego Police Department.

The Charley Project’s case entry was most recently updated on March 13, 2025 and likewise states that Dona Mae has never been found.

A search for later publicly documented developments through September 15, 2026 did not locate a credible announcement that Dona Mae’s remains have been recovered or identified. Accordingly, the unresolved part of the case is no longer who was convicted of her murder, but where Dona Mae’s remains are located and exactly what happened to her on May 6, 1979.

Anyone with information that could help locate Dona Mae should contact law enforcement rather than attempting an independent search or publicly identifying possible locations or individuals.

Very Brief Case Summary

Last seen: May 6, 1979
Location: Her home on Fennimore Lane, Muskego, Waukesha County, Wisconsin
Age: 38
Status: Murder victim; remains have never been recovered
Convicted: Husband John H. Bayerl
Conviction: First-degree murder, June 26, 2019
Sentence: Life imprisonment, August 30, 2019
Key circumstances: Dona disappeared following an argument with her husband. The family vehicle returned to the residence, but Dona vanished. She was not reported missing until May 9. Investigators later relied on circumstantial evidence, witness testimony, John’s statements and preserved blood evidence. Nearly 40 years after the disappearance, John was arrested, prosecuted and convicted. Dona’s remains remain missing.