On November 27, 1978, George Moscone, the 37th mayor of San Francisco, and Harvey Milk, a member of the San Francisco Board of Supervisors, were both shot and killed inside San Francisco City Hall by former supervisor Dan White. On the morning of that day, Moscone intended to announce that the Supervisor position from which White had previously resigned would be given to someone else. White, angered, entered City Hall before the scheduled announcement and first shot Moscone in the Mayor's office, then Milk in White's former office space, before escaping the building. Board of Supervisors president Dianne Feinstein first announced Moscone and Milk's deaths to the media, and because of Moscone's death, succeeded him as acting mayor.
White was charged with first-degree murder with circumstances that made him eligible for the death penalty. However, on May 21, 1979, White was convicted of the lesser crime of voluntary manslaughter and was sentenced to seven years' imprisonment, which resulted in the White Night riots and the abolition of the diminished capacity criminal defense in California. It also led to the commonly cited "Twinkie defense", as the defense had stated in passing that White's diminished capacity was partially evidenced by his consumption of sugar-laden junk food. White committed suicide in 1985, a year and a half after his release from prison.
Feinstein was elected by the Board of Supervisors to become the first female mayor of San Francisco on December 4, 1978, a title she would hold for the next ten years. She eventually became a United States senator for California until her death in 2023.
In the mid-1970s, San Francisco and the surrounding Bay Area were the scene of a series of anti-government bombings largely attributed to the New World Liberation Front, a leftist militant group. Members of the city government, including the mayor, had received bombs in the mail or were subjected to bomb threats, as was City Hall itself. On February 9, 1977, a tighter security regime began at City Hall to protect the mayor and members of the San Francisco Board of Supervisors, including locking most entrances, and providing security guards and metal detectors at public entrances, measures which had remained through 1978.
Prior to entering city politics, Dan White had been a member of both the San Francisco Police Department (SFPD) and the San Francisco Fire Department (SFFD). He and Harvey Milk were each elected to the Board of Supervisors in the November 1977 elections, which introduced district-based seats. The election ushered in "a range of legislators perhaps unmatched in San Francisco history in their diversity", including its first Chinese American (Gordon Lau), first unwed mother (Carol Ruth Silver), first black woman (Ella Hill Hutch), first homosexual (Harvey Milk) and first former firefighter (Dan White). All supervisors were sworn in on January 9, 1978, with Dianne Feinstein as the president of the board. The city charter prohibited anyone from retaining two city jobs simultaneously, so White resigned from his higher paying job with the SFFD. During 1978, White would try to supplement his salary as a Supervisor, totaling $9,600 per year (equivalent to $47,400 in 2025), with a food concession stand on Pier 39.
With regard to business development issues, the eleven-member Board was split roughly 6–5 in favor of pro-growth advocates including White, over those who advocated the more neighborhood-oriented approach favored by Mayor George Moscone, who was also elected in 1977. Debate among the board members was sometimes acrimonious and saw White verbally sparring with other supervisors, including Milk and Carol Ruth Silver. Further tension arose when Milk voted in favor of placing a group home within White's district. Subsequently, White would cast the only vote in opposition to San Francisco's landmark gay rights ordinance, passed by the Board on April 3, 1978 and signed by Moscone soon after.
A city charter amendment to raise the salaries of Supervisors was proposed in the summer of 1978, and a committee White was on stopped the amendment from going forward, in the context of the then-recent passage of California Proposition 13 in June. The low salary of the Supervisor position took its toll on White, and he tendered his resignation to Moscone on November 10. White stated that he could not support his family on only the Supervisor salary and that being forced to work two jobs was preventing him from adequately serving his constituents. White's resignation quickly renewed a call to amend the city charter to raise Supervisor salaries, this time proposed in White's name by Silver. His resignation would leave an open seat on the Board of Supervisors, a vacancy which would be filled by appointment by Moscone. This alarmed some of the city's business interests and White's constituents, as it indicated the mayor would tip the balance of power on the Board and appoint a liberal representative for the more conservative district.
On November 15, five days after resigning, White asked Moscone to return his letter of resignation (a letter that had already been accepted and filed by the Board) and expressed his intent to continue serving as a Supervisor after receiving loans from family and receiving encouragement from constituents. Moscone returned the letter, but on November 16, City Attorney George Agnost ruled that White had in fact resigned and was no longer on the Board, pending legal review, and whether White could be appointed back to the position from which he had just resigned was also an open question. Moscone stated that if "legal problems" in the finality of White's resignation arose, he would appoint White back to the seat, but in any case, some of the more liberal city leaders, most notably Milk and Silver, lobbied Moscone not to reappoint him. On November 17, Moscone stated that White's resignation was final and gave no indication that he was guaranteed to be re-appointed.
On November 18, news broke of the mass deaths of members of the Peoples Temple in Jonestown. Prior to the group's move to Guyana, the Temple had been based in San Francisco, so most of the dead were recent Bay Area residents, as was Leo Ryan, the United States Congressman who was murdered in the incident. The city was plunged into mourning, and the issue of White's vacant Board of Supervisors seat was pushed aside for several days. On November 21, Moscone confirmed that the city's legal position on White was that he had resigned, and further, that filling White's vacancy was a week away. He again made no guarantee of re-appointing White unless he was legally obligated to. White appeared to interpret Moscone's statements to mean that he would be re-appointed to his former position.
Rather than re-appoint White, Moscone decided to appoint Don Horanzy, a more liberal federal housing official, to White's former position on the Board. He scheduled a press conference to make this announcement on November 27, at 11:30 a.m.; advance copy had been sent to newspapers with late editions so they could begin preparing their stories.
White arranged for a former aide to drive him to City Hall on the morning Moscone was to make his announcement. He was carrying a five-round .38-caliber Smith & Wesson Model 36 Chief's Special loaded with hollow-point bullets (his service revolver from his work as a police officer), and ten extra rounds of ammunition in his coat pocket. White knocked on a basement lab window, and told a building engineer inside that he had misplaced his keys. White climbed into the window at about 10:25 a.m., thereby avoiding metal detectors and guards at public entrances.
White proceeded to Moscone's office, where the mayor was conferring with California Assemblyman Willie Brown. White requested a meeting with Moscone and was permitted to see him after the meeting with Brown ended.
As White entered Moscone's outer office, Brown exited through another door. Moscone met White in the outer office, where White requested again to be re-appointed to his former seat. Moscone refused, and their conversation turned into a heated argument over Horanzy's pending appointment. Wishing to avoid a public scene, Moscone suggested they retreat to a private lounge adjacent to his office. Witnesses later reported that they heard Moscone and White arguing, later followed by the gunshots that sounded like a car backfiring.