The people who created the murderous video are the people who support Trump. The video was shown at Trump's
This is who they are and what Trump has encouraged in his cultists:
The New York Times reported today that a video mashup depicting Trump slaughtering a church packed with his "fake news" enemies, from Barack Obama to the BBC, was shown last week to supporters at one of his Miami resorts.
The video, which includes the logo for Mr. Trump’s 2020 re-election campaign, comprises a series of internet memes. The most violent clip shows Mr. Trump’s head superimposed on the body of a man opening fire inside the “Church of Fake News” on parishioners who have the faces of his critics or the logos of media organizations superimposed on their bodies. ... The disclosure that the video was played shows how Mr. Trump’s anti-media language has influenced his supporters and bled into their own propaganda. Mr. Trump has made attacks on the news media a mainstay of his presidency, and he tweeted a similar — but far less violent video — in 2017. In recent weeks as he has confronted impeachment proceedings, he has ramped up his attacks on the news media, repeatedly calling it the “enemy of the people.”
It's evidently a scene from Kingsman: The Secret Service with Trump's head (among others) crudely superimposed on characters from the film. The mashup is incredibly, cringingly dorky— but it's also a video depicting the president on a killing spree in a church posted on the anniversary of one of America's most infamous white supremacist church massacres.