Brianna Elise Zerth pleaded guilty to domestic violence manslaughter after prosecutors dropped other charges in the case.

PEORIA, Ariz. — An Arizona woman who admitted killing her cousin with a hammer inside a Peoria home in 2022 has been sentenced to 21 years in prison after pleading guilty to domestic violence manslaughter.

Brianna Elise Zerth, 33, received the sentence Friday in the death of Peter McKenna Jr., also 33, after a case that began with a medical call, moved through an initial release, and later returned to court through a grand jury indictment. Court records show the sentence was the maximum allowed for the manslaughter count. Zerth received credit for 1,056 days already served, just under three years.

The case began just after noon on May 5, 2022, when Peoria police and first responders were called to a home near 112th Avenue and West Diana Avenue for a report of a dead man inside. Officers found McKenna with multiple blunt-force trauma injuries and pronounced him dead at the scene. Investigators soon identified Zerth as McKenna’s cousin and roommate. Police said the two had been drinking late the night before, on May 4, when an argument turned violent. Zerth later told investigators that parts of the night were “blurry,” and she said she woke up to find McKenna on the floor in a pool of blood.

Investigators said the scene inside the home showed signs of a violent fight and an attempted cleanup before the emergency call. Police said Zerth covered McKenna’s body with a jacket and tried to clean the area. Reports from the investigation said she tried to vacuum blood from the floor and picked up broken glass, telling police she was worried her daughter might step on it. Officers also found bloodstains throughout the home. Zerth later called police and reported that McKenna was “stiff and cold to the touch,” according to accounts of the investigation. Authorities said her 6-year-old daughter was home at the time but was not physically hurt.

The child’s presence became one of the earliest details released in the case and added to the urgency of the police response. Local reporting at the time said the girl told investigators that her mother had killed someone with a hammer. Police said the child had been told to wait outside during the incident. A neighbor who lived across the street described the scene in plain terms, saying, “What a sight that little one had to see.” Another neighbor, Gerard Giunta, said people nearby did not hear or see anything unusual before police arrived. “See this neighborhood. Nobody’s out,” Giunta said. “Other than that, this is a good neighborhood.”

Zerth was arrested after the killing, but the case did not move forward in a straight line. Prosecutors initially declined to formally charge her, saying they needed more evidence before taking the case ahead. The Maricopa County Attorney’s Office said at the time that police had submitted possible charges of second-degree murder, aggravated assault and evidence tampering. Prosecutors reviewed the material and sent the case back to law enforcement for more information. The office also said it had stayed in regular contact with McKenna’s next of kin and understood that the process could be frustrating.

The case returned in 2023 when a Maricopa County grand jury indicted Zerth on one count each of second-degree intentional murder, aggravated assault with a deadly weapon or dangerous instrument, and tampering, destroying or altering physical evidence. By then, the investigation had focused on the hammer attack, the blood found in the home, the cleanup efforts police said followed, and Zerth’s account of the fight. She later claimed McKenna had been strangling her during the struggle and had caused significant trauma. A medical examination corroborated that Zerth had significant injuries, according to reports tied to the case.

That self-defense claim helped shape the legal path that followed. The murder charge exposed Zerth to a more serious outcome if the case had gone to trial, while the defense had evidence that could raise questions about what happened during the fight. The plea agreement resolved those risks for both sides. Zerth pleaded guilty in April to one count of domestic violence manslaughter. In exchange, prosecutors dropped the aggravated assault and evidence tampering counts. The plea also replaced the second-degree murder allegation with a conviction on the lesser manslaughter charge.

The sentence marked the end of a case that had stayed open for more than four years after McKenna’s death. It also confirmed that Zerth would serve a long prison term despite the dropped counts. Court records listed 21 years as the maximum sentence available for domestic violence manslaughter. With 1,056 days of credit, Zerth’s remaining time will be reduced by the days she has already spent in custody. No trial is expected because the guilty plea resolved the criminal case.

Police have not publicly filled in every gap from the night of the killing. The exact moment when the argument became violent remains based on the accounts and evidence gathered in the home. Zerth’s memory of the fight was described as unclear, and McKenna was dead by the time help arrived the next day. What is clear from court records is that Zerth admitted to the fatal hammer attack and accepted a manslaughter conviction rather than face trial on the original charges.

The case now stands in the sentencing phase, with Zerth ordered to serve 21 years in prison and credited for time already served. The next milestone is the formal continuation of her prison term under the judgment entered after Friday’s sentencing.

Author note: Last updated July 8, 2026.