The death of Peter McKenna Jr. led to a delayed indictment and a 21-year term for his cousin.
PEORIA, Ariz. — A fatal fight inside a northwest Valley home has ended with a 21-year prison sentence for Brianna Elise Zerth, who admitted killing her cousin with a hammer in 2022.
The sentence closes a case that began in a residential area near 112th Avenue and West Diana Avenue, where neighbors later said they heard nothing unusual before police arrived. Peter McKenna Jr., 33, was found dead there on May 5, 2022. Zerth, his cousin and roommate, later pleaded guilty to domestic violence manslaughter and was sentenced Friday to the maximum prison term for that charge.
Police entered the home after an emergency call just after noon and found McKenna with multiple blunt-force trauma injuries. First responders declared him dead at the scene. The house then became the center of a homicide investigation that included bloodstains, broken glass, a hammer, statements from Zerth and the presence of her young daughter. Investigators said the fatal fight happened the night before, on May 4, after Zerth and McKenna had been drinking. The next day, police said, Zerth called authorities and described McKenna as “stiff and cold to the touch.”
The neighborhood details released after the killing painted a sharp contrast between the street outside and the evidence inside. Gerard Giunta, who lived nearby, said residents did not usually gather outside. “See this neighborhood. Nobody’s out,” Giunta said. “Other than that, this is a good neighborhood.” Another neighbor, reacting to reports that Zerth’s daughter had been at the home, said, “What a sight that little one had to see.” Police said the child was not physically hurt, but investigators reported that she told them her mother had killed someone using a hammer.
Inside the home, investigators said Zerth’s actions after the fight became part of the case. Police said she covered McKenna’s body with a jacket before calling for help. They also said she tried to clean the scene and attempted to vacuum blood from the floor. Reports said she picked up broken glass because she was afraid her daughter might step on it. Those details later supported an evidence tampering allegation. They also became central to how the case was publicly understood: not only as a violent family fight, but as a death followed by an alleged attempt to alter what first responders would find.
Zerth’s account gave investigators a partial timeline but left large gaps. She said she and McKenna had been up late drinking when they began to argue. She said the specifics were “blurry,” and she claimed she woke up to find him dead on the floor in a pool of blood. Police said she admitted swinging a hammer while fighting with him. Later reporting said she claimed McKenna had strangled her during the fight and caused significant trauma. An examination corroborated significant injuries to Zerth, a fact that made the charging decision more complicated.
The first prosecution decision did not result in immediate formal charges. Zerth was arrested after McKenna’s death, but prosecutors later declined to charge her at that stage, citing a need for more evidence. The Maricopa County Attorney’s Office said police had submitted possible charges of second-degree murder, aggravated assault and tampering with evidence. Prosecutors reviewed the file and referred it back to law enforcement. The office said it had regular contact with McKenna’s next of kin while the case remained under review.
More than a year after the killing, the case returned. In July 2023, a Maricopa County grand jury indicted Zerth on second-degree intentional murder, aggravated assault with a deadly weapon or dangerous instrument, and tampering, destroying or altering physical evidence. The indictment moved the case from a stalled early prosecution to an active felony case. It also put before the court the broader version of the allegations: that Zerth killed McKenna with a hammer, that a weapon was used in the assault and that evidence was altered after the attack.
The final resolution came through a plea agreement instead of a trial. Zerth pleaded guilty in April to one count of domestic violence manslaughter. Prosecutors dropped the aggravated assault and evidence tampering charges as part of the agreement. The plea meant no jury would hear the full evidence about the fight, the claimed strangulation, the child’s statement, the cleanup efforts or the medical findings. It also meant Zerth accepted criminal responsibility for McKenna’s death and faced sentencing under the manslaughter statute rather than the original murder count.
At Friday’s sentencing, the court imposed 21 years in prison and gave Zerth credit for 1,056 days already served. That credit amounts to just under three years. The prison term was not a minimum compromise within the manslaughter range; it was the maximum available for the count. The sentence also confirmed that the dropped charges would not be tried separately under the agreement. For a case that once appeared to pause after the first arrest, the judgment created a firm endpoint.
The record still leaves parts of the night known only through statements, injuries and physical evidence. No public trial tested Zerth’s memory claim against the state’s evidence. McKenna could not give his own account, and police have not released a complete moment-by-moment reconstruction. What remains is the official sequence established by the case: a drinking argument, a hammer attack, a delayed call for help, a revived prosecution, a manslaughter plea and a maximum sentence.
Zerth now faces the balance of a 21-year prison term, reduced by her credited time in custody. The case’s next milestone is the continued service of that sentence after the court’s final judgment.
Author note: Last updated July 8, 2026.