The film is based on the true bloodshed " Domhnach na Fola " that took place in Northern Ireland on January 30, 1972 . In 1998, the Northern Ireland peace agreement was signed, and the investigation into the matter was restarted in 2000. The investigation gradually revealed new evidence that "Bloody Sunday" was a planned massacre by the British army, and the British government in order to cover up the scandal. Some high-level officials were involved, and the British and Irish media launched a large-scale recollection, search and discussion on the matter. Two British TV stations have organized films about the incident, one is "Sunday" written and directed by Jimmy McGowan, and the other is "Bloody Sunday". The results of the survey were used in both films
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The author of the script, an eyewitness to "Domhnach na Fola", wrote a book about the incident that influenced the British government to re-investigate the incident. Director Greengrass was the first TV reporter to visit a prison in Northern Ireland against the British government in 1980, documenting a hunger strike in the prison. One of the hunger strikers was the same age as him, they grew up in the same land, listened to the same music, watched the same football games and TV shows, and the other went on a hunger strike for religion. The two kept in touch after the prison visit, and the prisoner's first letter to Greengrass began: "For me, it all started on that bloody Sunday." The director's original intention for the film was for everyone to come Going through this real nightmare together and facing mutual understanding directly can make a small contribution to the peace process. He tried to describe the whole event from the perspective of both sides, for which he also played a paratrooper role in the film
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