Killed were the popular mayor of San Francisco, George Moscone, and the nation's first openly gay elected official, Supervisor Harvey Milk.
On Wednesday, people attended a rally at City hall and then marched into the Castro District, where Milk operated a camera shop before he was killed.
On this day, each year, we relive San Francisco's darkest day.
The community groups held the march and rallies, just like they did when Moscone and Milk were killed.
Chris Moscone was only 16 when a police officer told him his dad was killed.
"And I said, 'what's going on?' And he said, 'Son, you don't know? Your father has expired.' Those were the words he said. I never really heard someone say that," Moscone said.
Nov. 27, 1978.
Dan White, a former firefighter who was elected to the Board of Supervisors, shot and killed the two men at City Hall.
He had resigned from the board earlier that month, but now wanted his seat back. White was angry that Moscone refused to re-appoint him. He packed his gun and went to City Hall.
Instead of going through the metal detectors, White slipped in through a door in the basement.
At the time, Willie Brown was a state assemblyman who was meeting with Moscone in the mayor's office. He left just 45 seconds before White entered.
"We were having coffee and George as usual said, you know, 'how do I just tell this guy it's all over? But I got to do it.' I walked out. Dan White walked in," Brown said.
Brown would learn later he also was on White's death list.
After he killed Moscone, White went to the supervisors offices, where he encountered Harvey Milk.
Gay rights activist Cleve Jones had just met with Milk that very morning
"I had been in City Hall that morning," he said. "Harvey sent me home to get a file I left in the apartment. And when I came back I saw his body."
At City Hall, chaos reigned.
A tearful Board of Supervisors President Dianne Feinstein broke the news to the public
Tens of thousands attended an impromptu march and rally that night at City Hall.
Chris Moscone says he's proud of his father's legacy, but most of all he misses him as a father.
"It's so sad that he wasn't able to see us grow up and his grandkids," Moscone said. "Because that's really what mattered to him, was his friends and family."
White turned himself into police. He was tried on first degree murder charges.
But his defense team successfully argued that his actions were caused by severe depression, even blaming junk food. That's why his defense was known as the "Twinkie Defense."
The jury convicted him of only voluntary manslaughter, a highly unpopular decision.
White served some of his time. He was paroled and later committed suicide.