SAN FRANCISCO -- The father of a Los Angeles Dodgers fan stabbed to death after a San Francisco Giants game last week made a public plea Sunday for independent witnesses to contact authorities.

Robert Preece spoke in front of AT&T Park's iconic Willie Mays statue before the Giants played the San Diego Padres. He said he believes bystanders used mobile devices to record a fight that ended with the death of his 24-year-old son, Jonathan Denver.

Michael Montgomery, 21, was released from custody Friday night after San Francisco District Attorney George Gascon said police had insufficient evidence to charge him in the death of Jonathan Denver, 24.

Gascon said police had not spoken with any independent witnesses who may have witnessed the fight Wednesday night.

"We have reason to believe someone recorded this," said Preece's sister, Jill Preece Haro, in a phone interview, adding that Denver's father and others with him saw bystanders using cellphone cameras. "We're calling on them to come forward to help both families find out what happened."

Haro said family members, including the victim's father who works as a security guard at Dodger Stadium, were motivated to travel from Southern California to make his public plea after Montgomery's release and Gascon's explanation.

"The San Francisco Police Department has provided us an initial investigation," Gascon said in a written statement Friday night. "However, not all witnesses have been interviewed, nor have any independent witnesses of the incident been interviewed. We have requested this and other evidence be collected before we can make an assessment on whether charges should be filed."

Police didn't return phone calls seeking comment.

Denver was stabbed to death Wednesday after attending the game with his brother, father and two others to celebrate his father's 49th birthday. Denver lived in Fort Bragg, a Northern California city about 170 miles north of San Francisco.

The group, many wearing Dodgers garb, left AT&T Park after the eighth inning to head to a nearby bar. At some point, they got into a shouting match over the Dodgers with Montgomery and a few friends who were bar-hopping in the trendy South of Market area. At least one was wearing a Giants cap.

"The back and forth, 'Go Dodgers!' 'Go Giants!"' Police Chief Greg Suhr said. "And it deteriorated from there."

Suhr said Montgomery made "incriminating statements" that led to his booking the night after the stabbing.

Montgomery's father told the Lodi News-Sentinel that his son was jumped during the fight, and he stabbed Denver in self-defence after Denver and others yelled "Giants suck." The father told the News-Sentinel that his son said Denver hit him over the head with a chair during the fight a few blocks from the stadium.

A second suspect was questioned and released by police Friday. Two others were being sought.

The stabbing was the latest incident over the years stemming from one of the most passionate rivalries in sports. Two years ago, Giants fan Bryan Stow suffered permanent brain damage when he was attacked in Los Angeles.

There was a moment of silence for Denver before the Dodgers hosted the Colorado Rockies on Friday night.

"I just can't understand how, sporting event aside, society's gotten like this," Giants general manager Brian Sabean said Friday. "It's bizarre to me."