A witness of the shootings in California has told how she saw the gunman just before he opened fire near a university, killing six.
She told the Associated Press that she thought the weapon was an Airsoft replica gun.
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Scotland Yard said the male youths will appear in custody at Westminster Magistrates' Court on Saturday.
Windy this weekend with gales across northwestern parts of the UK. Rain spreading southeast.
Greater Manchester Police said "inquiries are ongoing to fully understand the circumstances of the incident."