Scotland Yard has said it has submitted a file to the Crown Prosecution Service for consideration over whether any offences were committed in connection with the prank call made to the hospital where the Duchess of Cambridge was treated for morning sickness.
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Political parties across the country suspended their General Election campaigns following the Manchester Arena terror attack on Monday.
Investigators believe Mr Kushner has significant information relevant to their inquiry, officials told NBC News.
The men were detained as part of an investigation by MI5 and the Metropolitan Police's Counter Terrorism Command.