Labour has overwhelmingly held the seat of Middlesbrough with Andy McDonald elected the constituency's new MP with 10,201 votes.
The by-election was called following the death of Sir Stuart Bell.
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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.