Woman who killed cousin with claw hammer tried to secretly vacuum up the blood before calling for help, police say
An Arizona woman who admitted killing her cousin with a claw hammer and then attempting to clean up the crime scene before contacting authorities has been sentenced to more than two decades in prison.
According to court records and law enforcement officials, 33-year-old Brianna Elise Zerth pleaded guilty to domestic violence manslaughter in connection with the death of her cousin, Peter McKenna Jr., also 33. The fatal attack occurred in May 2022 at a residence in Peoria, Arizona. After entering her guilty plea in April 2026, Zerth was sentenced to 21 years in prison, the maximum sentence permitted for the offense under Arizona law.
Discovery of the Victim
Emergency Call Leads Police to Gruesome Scene
The case began on May 5, 2022, when officers with the Peoria Police Department responded to a medical emergency call shortly after noon at a home near 112th Avenue and West Diana Avenue.
Upon arriving at the residence, first responders found Peter McKenna Jr. deceased inside the home. Authorities observed that he had suffered multiple blunt-force trauma injuries consistent with a violent attack. He was pronounced dead at the scene. Investigators quickly learned that the suspect and the victim were cousins and had been living together as roommates.
What Happened Before the Killing
Night of Drinking Ended in Violence
According to court documents and police reports, Zerth and McKenna had spent the evening drinking alcohol together before an argument erupted.
Investigators said the dispute eventually turned violent. During questioning, Zerth reportedly admitted that she had swung a hammer during the confrontation. However, she later claimed that many details of the night were unclear because she had been drinking heavily and could not fully remember what had happened.
Claims of Self-Defense
As the investigation progressed, Zerth told authorities that McKenna had allegedly been strangling her during the altercation. She claimed the assault caused significant injuries to her.
Reports indicate that a medical examination found evidence of injuries that corroborated portions of her account regarding physical trauma. The circumstances surrounding the struggle ultimately became a significant factor in the legal proceedings that followed.
Attempted Cleanup Before Calling Police
Suspect Covered Victim and Tried to Remove Evidence
One of the most disturbing aspects of the case involved Zerth’s actions after the fatal attack.
According to investigators, rather than immediately contacting emergency services, Zerth allegedly attempted to clean the crime scene. She reportedly covered her cousin’s body with a jacket and began removing signs of the violent struggle.
Authorities said she tried to vacuum up blood from the residence and also attempted to clean up broken glass scattered around the home. Police later cited these actions as evidence of an effort to conceal what had happened.
Concern About Daughter’s Safety
Zerth reportedly told investigators that one reason she picked up broken glass was because she was worried her young daughter might step on it.
Court records show that her daughter was present at the home during the incident. Investigators later learned that the child had been instructed to wait outside during portions of the confrontation. Fortunately, the girl was not physically harmed.
Child’s Statement Played a Key Role
Young Daughter Described the Killing
Police reports revealed that Zerth’s 6-year-old daughter provided investigators with crucial information.
According to authorities, the child told investigators that her mother had killed someone using a hammer. The girl’s account became an important part of the investigation as detectives worked to determine exactly what had occurred inside the residence.
The Call to Police
Authorities Contacted After Victim Was Already Dead
After allegedly attempting to clean portions of the scene, Zerth eventually contacted authorities.
She reportedly told police that McKenna was “stiff and cold to the touch,” indicating that he had been dead for some time before the call was made. When officers arrived, they found blood evidence throughout the residence and began documenting the scene.
Initial Charges and Legal Developments
Murder Charges Filed
Following the investigation, prosecutors initially pursued serious charges against Zerth.
She was originally indicted on counts including:
- Second-degree intentional murder
- Aggravated assault with a deadly weapon or dangerous instrument
- Tampering with, destroying, or altering physical evidence
Authorities alleged that the claw hammer used during the attack qualified as a deadly weapon in the case.
Earlier Release Due to Lack of Evidence
The legal process took several unexpected turns.
According to reports, Zerth was initially arrested after the killing. However, prosecutors later declined to formally pursue charges at that stage because investigators believed there was insufficient evidence to move forward. As a result, she was temporarily released while authorities continued reviewing the case.
Plea Agreement Reached
Guilty Plea to Manslaughter
Years after the fatal confrontation, Zerth entered into a plea agreement with prosecutors.
In April 2026, she pleaded guilty to one count of domestic violence manslaughter. In exchange for the plea, prosecutors agreed to dismiss the additional charges involving aggravated assault and evidence tampering.
Maximum Sentence Imposed
On June 5, 2026, the court sentenced Zerth to 21 years in prison.
Court records show that the sentence represented the maximum punishment available for domestic violence manslaughter under Arizona law. She also received credit for approximately 1,056 days already spent in custody, which amounts to nearly three years.
Community Shocked by Brutal Family Tragedy
Neighbors told local media they had not noticed anything unusual coming from the residence before police arrived. The killing nevertheless stunned the neighborhood, particularly because it involved family members living together under the same roof.
The presence of Zerth’s young daughter during the events added another tragic dimension to a case that prosecutors described as a deadly domestic dispute fueled by alcohol, violence, and a failed attempt to clean up the aftermath before authorities were called.
Case Conclusion
The death of Peter McKenna Jr. brought an end to a years-long legal saga that began with a violent argument inside a Peoria home in May 2022. Investigators alleged that Brianna Zerth struck her cousin multiple times with a claw hammer, attempted to vacuum blood and clean the scene afterward, and only later contacted police.
With her guilty plea and 21-year prison sentence, the criminal case has now reached its conclusion, though the circumstances surrounding the fatal confrontation remain a sobering example of how a family dispute escalated into a deadly act of violence.
