Police said late Wednesday night that the 22-year-old man was arrested earlier that morning by specialist royal police officers.
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Palace officials declined to say whether the queen was told about the incident.
According to police, the alleged intruder wasn’t carrying a weapon, and the incident is not seen as related to any extremist threat.
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He was held on suspicion of trespassing at around 2 a.m. on Wednesday by specialist royal police officers, the Metropolitan police said.
“The 22-year-old man was arrested at approximately 2 a.m. on Wednesday, 10 July, by officers from the Met’s royalty and specialist protection command after he climbed over the front gates at Buckingham Palace,” a Metropolitan spokeswoman said.
Police initially declined to disclose whether there would be a review of security after the incident.
The Directorate of Media and Communication for the Metropolitan Police published a statement on their website. “A man who was arrested on suspicion of trespass, contrary to section 128 of the Serious Organised Crime and Police Act 2005, has been released under investigation,” the statement reads.
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The suspect is in police custody. He hasn’t been charged or identified.
—With files from the Associated Press