Antonine Kendrick, 35, is now facing second-degree murder charges after the man succumbed to his injuries in the hospital on August 5.
Due to privacy reasons, the man's name has not been released.
RadarOnline.com previously reported on the incident which took place around 4:40 PM on July 26 in the fast food chain's Prescott Valley location.
Police said the elderly customer had complained about his food order. Moments later, Kendrick came out from behind the service counter and struck the customer in the head as he licked his Frosty, knocking him onto the ground and leaving him unconscious.
Kendrick then gazed down at the man before walking behind the counter, picking up a few items and making his exit.
After being tended to by central Arizona fire and medical authority, the man was airlifted to a Valley hospital in critical condition. As a result, Kendrick was hit with aggravated assault charges which have since been raised amid news of the man's death.
Kendrick was arrested and booked on July 26 at 8:52 PM, RadarOnline.com can confirm.
He is still in custody at this time, according to online jail records.
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"That was a pretty hard hit. That was a Mike Tyson hit," one customer said after seeing graphic footage of the assault, per local outlet AZ Family. "The customer didn't touch him, so he had no right to touch the customer, period, end of story. I just think that's horrible and wish it didn't happen. It puts a bad light on our entire society."
Another resident said they had never witnessed anything like it over the past two decades.
"It's mellow up here, you don't have that kind of stuff," they said. "It's a shame. I feel for the guy that got hit. It's not right."
A third local added, "Unfortunately, we just need to be cautious and just care for each other and be respectful and try to hold back our frustrations and not get this violent."