Cleveland Police are investigating after beach cleaners discovered what could be a grenade at Seaton Carew beach.
Bomb disposal teams from Catterick Garrison are on the way to the scene.
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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.