No one seems to know why it happened.
Surveillance video shows the fateful encounter: as he was waiting for a Chicago bus just before 5 a.m. Thursday, 88-year-old Arthur Hearn was knocked to the ground by a young man, WLS-TV reported.
Hearn died of head injuries on Sunday evening, WLS reported, and his death has been ruled as a homicide.
The unknown man and his female accomplice hailed nearby police after their encounter with Hearn, WLS noted, but the pair fled soon afterwards and the events that led to the pre-dawn altercation.
Hearn's community mourned his death.
"He was a great man," said Kelvin McGahen, a barber who had worked with Hearn at Farrell's Barbershop. "I can think of countless times he's helped me out of situation that I may have been in, whether spiritually, mentally or financially or whatever the case may be. He was a wonderful person."
Arthur Hearn. (Image via WLS-TV)
One of Hearn's family members issued a message to the man who fatally pushed Hearn, saying, "Just know that you have taken away a mentor to the community, and how many lives that you have really destroyed and affected."
Relatives also speculated that Hearn would have fought back Thursday morning, noting that in 1996, Hearn took a bullet to his leg while he was saving a woman from a sexual assault.
"He was built like a horse," one family member said. "I mean, there was nothing frail about him. He took awesome care of himself inside and out."
The family may still be seeking answers, but as of Tuesday, WLS reported, no one was in custody in connection with Hearn's death.
Follow Zach Noble (@thezachnoble) on Twitter