The president was friends with Epstein in the 1990s and early 2000s. Trump has never been officially accused of wrongdoing in connection with the deceased paedophile financier.
The nine-minute video was projected from a hotel room window opposite the royal residence by members of Led By Donkeys, a UK-based campaign group.
It focused on the history of Trump’s links to Epstein, including the release by the US lawmakers last month of an alleged letter from Trump to Epstein.
At the time of the arrests, a spokesperson for the group said the police response seemed “ridiculous” and “heavy-handed” when no one had been detained for previous projections.
“I think they’ve been arrested for embarrassing Donald Trump,” the spokesperson added.
Thames Valley Police previously launched an investigation after saying officers responded “swiftly” to stop the projection on the castle and arresting the men on 16 September.
On the same day, Trump landed in the UK for an unprecedented second state visit. He met King Charles at Windsor on 17 September, with the visit largely taking place behind the walls of the castle.
Some protesters gathered in Windsor ahead of the visit and a significant police operation was in place in the town.
The Metropolitan Police said more than 1,600 officers were deployed in central London in response to protests by the Stop Trump Coalition.
