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Dead suspect in shooting of mediation opponents was litigious, had anger issues, lawyer says

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Updated: A man who authorities say committed suicide after shooting a corporate attorney and his client after a law firm mediation session Wednesday in Phoenix was reportedly litigious and had anger-management issues.

Before shooting attorney Mark P. Hummels, 43, and client Steven Singer, 48, who both died, Arthur Douglas Harmon, 70, was known as an unpleasant litigant who didn’t hesitate to sue, according to Fox 10 News and KPHO.

Unlike family-court cases, which are known for being emotionally charged, the dispute at issue in the case between Harmon and Singer was a business matter, attorney Colin Campbell pointed out to KPHO. Campbell, a former Maricopa County Superior Court judge, is a colleague of Hummels at Osborn Maledon.

Nonetheless, Harmon reportedly shot the attorney and his client in a parking lot after the mediation session. In a letter to Hummels related to the case, Harmon had used profanity and told the attorney: “I won’t rest until I see you behind bars,” the KPHO article says.

Another area lawyer, David Panzarella, dealt with Harmon in a 2008 case. Harmon was litigious and had been involved in nearly a dozen prior civil suits, he told Fox 10 News.

“He represented himself and he was a particularly unpleasant man, not only lawyers and staff in our office will remember his name for years,” Panzarella said. “When his name came up today, we certainly recognized it.”

Lawyers often try to back off on particularly difficult cases, but it can be hard to predict how far an angry litigant is prepared to go, Panzarella continued.

“You can tell that they are getting so agitated, but you wonder when it’s all over if they are going to meet you in the parking lot.”

Updated Feb. 1 to report that Mark Hummels has died of his wounds.

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