It began as a verbal altercation on a bus, police said.
Authorities released the video in hopes of locating witnesses to the attack.
Homicide detectives took over the investigation and determined a woman had been arguing with people on the bus.
Witnesses say Bishop pushed the man out of the bus door after getting into an argument with the victim and other passengers. He initially refused treatment but later went to the hospital, police said.
As Fournier used his walker to exit at 13th and Fremont streets, police say Bishop pushed Fournier forcefully with two hands. The Clark County Coroner-Medical Examiner told CNN he died as a result of complications from blunt force injuries to his torso, and ruled his death a homicide.
Before the shove, Fournier-wearing a ball cap and red jacket-can be seen in the video exchanging words with a woman who is standing at the front of the bus.
But as he prepares to step off the bus a person shoves him from behind.
After the alleged shoving, Bishop reportedly fled the scene. Police officials believe that Bishop had been yelling profanities at people on the bus.
Ken Mallen told the station he knew Fournier and that his death is causing "several financial problems for his wife", who is disabled.
Cadesha Bishop, 25, was arrested on May 6, more than a month after the March incident.
"No matter what his age, she should not have done that".
The family then notified Las Vegas Police on May third. "Very nice, religious person", he added.