Robert Preece spoke outside AT&T Park before the Giants played the San Diego Padres. He was flanked by family members who handed out fliers to fans streaming into the stadium.
"We need your help," one flier stated, "that can help bring forth the truth."
The 49-year-old believes bystanders recorded the fight with mobile devices. He urged anyone who may have shot video on a cellphone or at least witnessed the deadly altercation to call San Francisco police.
"Losing a child is a heartache no parent should have to endure," said Preece.
Michael Montgomery, 21, of Lodi is suspected of fatally stabbing Preece's 24-year-old son, Jonathan Denver. He, however, was released from jail Friday.
Denver was stabbed to death Wednesday after attending the game with his brother, father and two others to celebrate his father's 49th birthday.
San Francisco's district attorney says police have not collected enough evidence to warrant criminal charges against Montgomery.
Denver's mother, Diana Denver, said in a prepared statement that she was angered by Montgomery's release and what she called "the negligence of our justice system."
The suspect's father told other media outlets that his son was acting in self-defense. He claims Denver hit his son over the head with a chair and that Montgomery stabbed Denver in self-defense.
Police have not interviewed any independent witnesses since the altercation.
Denver's family hopes video of the incident, if it exists, will clarify what really happened.
Preece, who is a security guard at Dodger Stadium, says he lost his son too soon.
"I will always cherish the time me and my son spent here at the game. More than once that night, Jonathan told me how much he loved me," said Preece who was there Wednesday when the stabbing occured. He didn't speak on what he witnessed during Sunday's conference.
Police say Denver's group, wearing Dodger gear, went to a bar after the game and got into a shouting match with Montgomery's group over the team's rivalry. The fight escalated from that point, according to police.
"The back and forth, 'Go Dodgers!' 'Go Giants!'" Police Chief Greg Suhr said. "And it deteriorated from there."
Preece says his family and the Montgomery's need closure.
"The Montgomery family is likely suffering as well," said Preece. "I am making a plea to the public asking that anyone who may have witnessed the incident to come forth so that both families can have some measure of closure."
The 49-year-old also thanked everyone for their condolences including the Los Angeles Dodgers and the San Francisco Giants.
The investigation remains ongoing.
The Associated Press contributed to this report.