The Brief
- A judge has ruled Matthew Dieringer incompetent to stand trial for the first-degree murder of Frank Quaranta, a 67-year-old man in Scottsdale.
- A mental health expert diagnosed Dieringer with delusional disorder and a paranoid personality style, among other conditions.
- He is assigned to a competency restoration program within Maricopa County, with a standard timeframe of 15 months.
PHOENIX
An accused killer, characterized by Scottsdale police as “charismatic and manipulative,” is currently not facing trial after a judge ruled him incompetent. Matthew Dieringer, 36, was arrested over a year ago for allegedly beating Quaranta to death in his home, suffering serious injuries such as skull fractures and broken ribs. Dieringer had been on supervised probation for previous theft charges when the murder occurred.
The Backstory
Quaranta, who worked at a heat relief center, met Dieringer while he was homeless. Dieringer has a history of violent behavior, including an incident where he slammed a woman’s dog to the ground and attempted to punch a man shortly after.
His past includes severe animal cruelty charges in Colorado, where he mutilated two dogs in 2020.
Dig Deeper
Dieringer has been described as disruptive and erratic, believing himself to be a target of conspiracy due to his self-proclaimed celebrity status. During a January 2026 hearing, he claimed the proceedings were “all scripted.”
Under Arizona law, a defendant is deemed incompetent if mental illness prevents them from understanding court proceedings or assisting in their defense. Experts provided mixed assessments regarding his competency; while two found him competent, a third diagnosed several mental health conditions.
What We Know
When unmedicated, Dieringer exhibits uncooperative and irrational behavior, alongside delusional thoughts. Despite finding him competent in prior cases, current evaluations suggest different conclusions.
What We Don’t Know
There is uncertainty surrounding when Dieringer may regain competency, as there is no clear evidence he will be restored within the 15-month standard timeframe set by the judge.
What’s Next
Dieringer is currently enrolled in the competency restoration program, with his next court hearing scheduled for November 12.
The Source
Information has been compiled from Scottsdale police, court records, and previous reporting by FOX 10.
