Out screenwriter Dustin Lance Black said Tuesday that he “doubted every day” that his Academy Award-winning film about Harvey Milk would be made.

Tuesday marked 40 years since Milk was murdered at San Francisco City Hall.

Milk was the first openly gay elected official of a major U.S. city. He was elected to the San Francisco Board of Supervisors in 1977 on a pledge to back gay and lesbian rights. The following year, Milk was killed by Dan White, a former supervisor, on November 27.

Director Gus Van Sant's 2008 film Milk was based on Milk's life. Sean Penn played Milk in the film, while Josh Brolin portrayed White. Black won an Oscar for his screenplay.

In an interview with Focus Features, the studio which released the film, Black said that during the film's production “we doubted every day that our green light would last until we wrapped.”

“For many, the film is increasingly being seen as the first part of a larger project to revive our lost history. So much of the rich history of the LGBTQ+ community has been lost. No, lost is too passive a word. Buried or destroyed is more accurate,” Black said.

“Things have changed so massively in 10 years. Back then, getting people interested in stories that just had an LGBTQ+ character was incredibly difficult, much less a story that took our lives seriously. A mainstream film that had LGBTQ+ characters at its core seemed impossible. There were few exceptions,” he added citing Will & Grace, Ellen and Brokeback Mountain as a few examples.

Black is married to British diver Tom Daley. Together they recently welcomed their first child.

(Related: Tom Daley, Dustin Lance Black say they'll keep son “completely private.”)