In early September 2025, police arrested Matthew S. Dieringer in connection with the killing of 67-year-old Frank Quaranta at a residence in Scottsdale, Arizona.
What makes the case particularly disturbing is that Dieringer is not new to violent crime. Dieringer’s criminal record shows a 2020 conviction in Colorado for killing and dismembering dogs, which were his roommate’s pets.
Quaranta’s murder
Arizona authorities found Quaranta deceased from apparent blunt-force trauma on September 1, 2025, after a welfare check call prompted forced entry into his home. Investigators called it a targeted attack carried out by Dieringer, a man Quaranta had been sheltering after meeting him through a local outreach effort helping unhoused individuals. Authorities say Dieringer has lived unhoused in the past.
Scottsdale PD said in a press release, “He has a history of experiencing homelessness, and has been described as manipulative and charismatic, often befriending others to assist him with a place to stay.”
After Quaranta died, a citizen recognized Dieringer in Phoenix and alerted police. Once in custody, a presumptive DNA match connected Dieringer to the blood found at the crime scene.
Dieringer’s gruesome 2020 crime
Back in 2020, in Colorado, Dieringer targeted a 7-year-old Australian Cattle Dog named “Suka,” who died of blunt-force trauma, and a black dog named “Hayoka,” whom he allegedly dismembered.
In that case, law enforcement issued a felony warrant for two counts of aggravated cruelty to animals, a class 6 felony. After being located at a motel in Arapahoe County, Colorado, Dieringer was arrested, held on a $10,000 cash-only bond, and ultimately sentenced to 18 months in prison.
Now held on a $3 million bond, Dieringer has not formally entered a plea in the Scottsdale murder case. During his first court appearance on September 7, 2025, Dieringer voiced his disagreement with the proceedings, calling them “illegal” and insisting, “there’s no truth” to the accusations against him. His next scheduled court dates are September 12 for the murder charge and September 15 for the probation violation related to yet another 2024 theft case.
