The fatal fight between cousins ended with a guilty plea after prosecutors first sought more evidence.
PEORIA, Ariz. — A medical call to a Peoria home in 2022 became a homicide case after officers found Peter McKenna Jr. dead from blunt-force injuries and later arrested his cousin, Brianna Elise Zerth.
Four years later, the case has ended with a 21-year prison sentence for Zerth, 33, who pleaded guilty in April to domestic violence manslaughter. The sentence handed down Friday was the maximum for that charge, according to court records. The case drew attention because police said Zerth tried to clean the scene, including by vacuuming blood, before calling for help.
The first official step came shortly after noon on May 5, 2022, when Peoria officers were sent to a residence near 112th Avenue and West Diana Avenue. The call was not first described as a murder scene. It was a report of a dead man inside a home. First responders entered and found McKenna, 33, with signs of multiple blunt-force trauma injuries. He was pronounced dead at the home. Investigators then worked backward from the scene, the people who lived there and the account Zerth gave after police arrived.
Police said Zerth and McKenna were cousins and roommates. Court documents from the early case said they had been drinking heavily and got into an argument the night before officers arrived. Zerth admitted swinging a hammer during the fight, police said. She also told investigators she did not remember part of what happened. Her account, as later described in reports, was that she woke up and found McKenna dead on the floor in a pool of blood. She told police the details were “blurry,” a word that became central to the investigation because it left the timeline incomplete.
The condition of the home gave investigators more to examine than Zerth’s statement. Officers reported bloodstains throughout the house. Investigators said Zerth covered McKenna with a jacket after finding him on the floor. She also tried to clean the area and remove items from the scene, police said. The cleanup effort included an attempt to vacuum blood and a decision to pick up broken glass. Zerth told investigators she was worried her daughter might step on the glass. Police said she called authorities only after that, telling them McKenna was “stiff and cold to the touch.”
The child in the home was 6 years old at the time and was not physically injured, officials said. Her presence added a separate layer to the early police account. Local reporting said the child told investigators that her mother had killed someone with a hammer. Police said the child had been told to wait outside while the incident unfolded. Neighbors later said the home did not stand out to them before officers arrived. One neighbor said he did not hear suspicious noise. Another described the surrounding area as a quiet place where people were often not outside.
Although Zerth was arrested soon after McKenna was found, the case stalled at first. Prosecutors did not immediately move ahead with formal charges after reviewing the original police submission. The Maricopa County Attorney’s Office said the submitted charges had included second-degree murder, aggravated assault and tampering with evidence, but prosecutors referred the case back to law enforcement for more information. The office said it had regular contact with the next of kin and acknowledged the criminal justice process could be frustrating for families waiting for answers.
The delay did not close the case. In July 2023, a Maricopa County grand jury returned an indictment charging Zerth with second-degree intentional murder, aggravated assault with a deadly weapon or dangerous instrument, and tampering, destroying or altering physical evidence. The indictment put the case back on a trial track. It also showed that investigators and prosecutors had gathered enough evidence to present the matter again. By that point, the case file included the hammer allegation, the condition of the home, Zerth’s cleanup statements, the child’s reported statement and the medical findings tied to both McKenna and Zerth.
Zerth’s defense account included a claim that McKenna had strangled her during the fight. Reports said an examination corroborated significant trauma to Zerth. That detail complicated the original murder case because it raised questions about the struggle inside the home and the level of criminal intent prosecutors could prove. Prosecutors still pursued the charges after the grand jury indictment, but the final conviction came through a plea rather than a trial. The plea narrowed the case to manslaughter while keeping the domestic violence designation.
Under the plea agreement, Zerth admitted to attacking McKenna with a hammer on May 4, 2022. Prosecutors dropped the counts alleging aggravated assault with a deadly weapon and evidence tampering. The second-degree murder charge also did not remain as the final conviction. Instead, Zerth pleaded guilty to one count of domestic violence manslaughter. The agreement avoided a trial that would have required jurors to sort through the drinking, the claimed memory gap, the alleged strangulation, the child’s presence and the actions police said Zerth took before she called 911.
At sentencing, the court imposed 21 years in prison and credited Zerth with 1,056 days already served. That credit equals just under three years in custody. The sentence brought the criminal case to a close without testimony before a jury. For McKenna’s family, it marked the first final judgment after years of filings, a declined initial prosecution, a later indictment and a negotiated plea. For Zerth, it meant a long prison term on a conviction that legally recognized the killing but did not carry the original murder label.
The official record now leaves some details unanswered. Police have not publicly established a complete minute-by-minute account of the fight inside the home. Zerth’s stated memory gap and McKenna’s death before first responders arrived limit what can be known from direct accounts. The physical evidence, the statements described in court records and the guilty plea supplied the basis for the sentence. The case stands closed in criminal court unless a later filing changes the judgment.
Zerth remains sentenced to 21 years in prison, reduced by credit for time already served. The next formal step is the continued administration of that sentence under Arizona corrections records.
Author note: Last updated July 8, 2026.