Denver's family tells ABC7 News they will not let his death be forgotten, despite Gascon's decision not to prosecute the man who fatally stabbed the Dodger fan last September.
"We are upset and outraged," his aunt said. "Jon lost his life and nothing is happening."
Denver's family says they are deeply disappointed by Gascon's decision not to charge 21-year-old Michael Montgomery.
"I'm angry with the system," Denver's mother Diana said. "I want justice for my son."
Denver, his brother Robert Preece and friend Joey House were all walking near 3rd and Perry streets after a Giants-Dodgers game. They claim they were jumped by Montgomery and his group.
The DA isn't so sure, but does concede the Montgomery fatally stabbed Denver.
In a statement, Gascon said: "Mr. Denver punched Mr. Montgomery. At, or near the same time, the victim's brother, swung a collapsible aluminum chair at Mr. Montgomery striking Mr. Montgomery in the head. Both the victim and his brother substantially outweighed Mr. Montgomery by 50 and 100 pounds respectively."
In October, Preece told ABC7news he did swing the chair, but only to defend his brother and House, who by then had been knocked unconscious.
"I just think something needs to happen," House said. "This guy can't just walk around on the streets. He's too dangerous.">
House says he asked the DA to press charges against Montgomery, but was told the case is now closed.
Denver's family says their fight is far from over.
"We just feel as a family, it's not fair," Preece said.
The San Francisco District Attorney's Office did not respond to requests for an on camera interview.
ABC7 News could not reach Montgomery or his family.