British police said Monday they were investigating a video linked to a man armed with a crossbow who was arrested at Windsor Castle on Christmas Day.

The video, obtained by The Sun newspaper, showed a masked person in a dark hoodie holding a crossbow and addressing the camera with a distorted voice, saying they wanted to “assassinate” Queen Elizabeth II.

The Sun said the video was sent from the suspect’s Snapchat account shortly before he was arrested.

Police said they arrested a 19-year-old man within the grounds of Windsor Castle after a security breach took place on Christmas morning. Officers found a crossbow after searching the man.

They said the man was suspected of breaching a protected site and possessing an offensive weapon, but that he did not enter any buildings.

Police said the suspect, who has not been named, is in custody under the Mental Health Act and “in the care of medical professionals.”

Detectives “are assessing the contents of the video,” police said.

A Buckingham Palace spokeswoman declined to comment.

The queen, 95, spent the Christmas holidays at Windsor, west of London, having decided not to stay at Sandringham, the royal estate in eastern England where she traditionally spends the festive season with family.