A senior police officer said he was concerned for the safety of three young boys from Sunderland who are missing after apparently catching a Metro train to Newcastle.
They left their home together and did not return.
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Sandiford, a former legal secretary originally from Redcar, was convicted of drug smuggling offences and sentenced to death in 2013.
Durham Crown Court heard that one of the male victims suffered a triple-fractured jaw, while left lying in the gutter, unconscious.