Murderer Matthew Dieringer was a convicted dog killer

Murderer and dog killer
Credit : Teller County Sheriff's Office
Name	Matthew Stephen Dieringer
Age	35 (at time of 2025 arrest)
Occupation	Unemployed / Transient
Known Identifiers
Status	Incarcerated
Involvement	Perpetrator of the 2020 aggravated animal cruelty case in Colorado and the primary suspect in the 2025 murder of Frank Quaranta in Arizona.
Punitive Measure	Sentenced to 18 months for animal cruelty; held on a multi-million dollar bond for the murder charge.

Matthew Stephen Dieringer (born c. 1990) is an American transient felon whose criminal history serves as a case study in the escalation from extreme animal cruelty to homicide. In 2020, he was convicted of aggravated animal cruelty for beating and dismembering his roommate's two dogs in Teller County, Colorado. In September 2025, he was arrested and charged with the murder of 67-year-old Frank Quaranta in Scottsdale, Arizona. Dieringer's case is a powerful example of the "graduation hypothesis," which posits a direct link between violence against animals and subsequent violence against humans.

Perpetrator profile

A native of Pueblo, Colorado, Matthew Dieringer is a transient individual who authorities describe as "manipulative and charismatic." He has a consistent modus operandi of befriending individuals, often through charitable organizations, for the sole purpose of securing shelter. This predatory social strategy allowed him to gain access to the homes of his victims in both Colorado and Arizona. His transience complicates law enforcement tracking, allowing him to move between communities, exploit new individuals, and flee after committing offenses.

Precursor crime: 2020 Colorado animal cruelty

In July 2020, while living with a roommate in Teller County, Colorado, Dieringer committed an act of extreme brutality against his roommate's two dogs. The act was seen as a way of inflicting emotional terror on the human owner by proxy.

• Suka, a 7-year-old Australian Cattle Dog, was beaten to death. A necropsy confirmed the cause of death was blunt force trauma.
• Hayoka, a black dog, was also killed and subsequently dismembered.

• Canine Victims
• 
  Hayoka
• 
  Suka

The combination of explosive rage ("hot" violence in the beating) and methodical mutilation ("cold" violence in the dismemberment) is considered the hallmark of a particularly dangerous offender.

After a felony warrant was issued, Dieringer became a fugitive. He was captured on July 26, 2020, at a Days Inn Motel in Centennial, Colorado, after a citizen tip and tracking of his "digital footprint." He was convicted of two felony counts of aggravated animal cruelty and sentenced to 18 months in prison. In a perplexing judicial outcome, he was credited with 705 days (approx. 23 months) of time served, which exceeded his sentence and resulted in his release.

Escalation: 2025 Arizona homicide

In 2025, Dieringer was living in Arizona. According to court records, a few months prior to the homicide, he attacked three different people and their pets in a single day in downtown Phoenix.

Later, he met 67-year-old Frank Quaranta at a church homeless outreach event. Leveraging his charismatic persona, Dieringer befriended Quaranta, who compassionately offered him a place to live in his Scottsdale home.

On September 1, 2025 (Labor Day), colleagues requested a welfare check after the reliable Quaranta failed to show up for work. Police entered his home and found him deceased. Investigators immediately deemed it a homicide and a "targeted attack." The cause of death was determined to be "apparent blunt force trauma," the same method of violence used to kill the dog Suka in 2020, pointing to a consistent behavioral signature.

Dieringer again became a fugitive. On September 6, 2025, a citizen recognized him from media reports and alerted Phoenix police, leading to his arrest. He was initially booked on a probation violation from a 2024 theft case. During his initial court appearance on September 7, he exhibited manipulative behavior, first claiming mistaken identity ("I believe that you are being given wrong information entirely about me and my name"), then challenging the legality of the proceedings, and finally feigning piety by telling the judge, "God bless you." He is being held on a multi-million-dollar bond, with prosecutors citing strong DNA evidence linking him to the crime scene.

Criminological significance

Dieringer's case is a textbook illustration of "The Link," the well-established criminological connection between animal cruelty and interpersonal violence. The 2020 animal killings served as the "training ground," desensitizing him to extreme violence and allowing him to rehearse the lethal rage that would later be deployed against a human victim. The judicial system's failure to recognize the 2020 zoosadism as a critical red flag for potential homicide, resulting in a short sentence, allowed a predictable escalation of violence to occur, culminating in the death of Frank Quaranta.