Arthur Harmon opened fire at the end of a mediation session at a Phoenix office complex on Wednesday, killing one person and wounding two others.
Hummels, 43, was listed in critical condition Wednesday at John C. Lincoln North Mountain Hospital.
His law fim, Osborn Maledon, sent a statement around noon Thursday that included the following:
Our friend and partner, Mark Hummels, was severely injured in yesterday's senseless shooting. We have been informed that Mark will not survive from the shooting.
We are devastated at this news about our beloved friend. Our deepest sympathy and support pour out to his wife, Dana, and their two children. The trust and affection Mark inspired in every reach of our law firm and with his clients are a lasting testament we will always cherish.
Mark Hummels is the best kind of lawyer – a man who is highly capable in his practice and caring to his core about his community. Still in the early years of his career, Mark has earned many accolades for his skill as an attorney.
On Hummels' biography pages, the firm writes:
Before embarking on his legal career, Mark worked as a politics and government reporter for the daily Santa Fe New Mexican newspaper. He earned the highest score on the July 2004 Arizona bar exam.
Investigators identified the man who died Wednesday from his gunshot wounds as Steve Singer, 48.
Singer was the CEO of Fusion Contact Center in Scottsdale and was in a legal dispute with the suspected shooter.
Hummels is an attorney who was representing Singer.
Sources told ABC15 that Singer leaves behind a wife and two children.
"He will be missed," a coworker said.
The final shooting victim, Nichole Hampton, 32, was shot in the hand and is expected to make a recovery, according to police.