The Metropolitan Police are investigating a video linked to a man who was arrested at Windsor Castle while in possession of a crossbow. The video, obtained by The Sun, appears to show a masked figure in a dark hoodie holding a crossbow and addressing the camera with a distorted voice, saying they wanted to “assassinate the Queen” in a “revenge” mission. It comes after a 19-year-old man was arrested on Christmas Day within the grounds of the castle in Berkshire where Queen Elizabeth II is in residence. The man, from Southampton, was arrested on suspicion of breach or trespass of a protected site and possession of an offensive weapon. Police said he has since been sectioned under the Mental Health Act and remains in the care of medical professionals. A spokesperson from Scotland Yard said: “Security processes were triggered within moments of the man entering the grounds and he did …