The jury at Lewis Crown court heard how Lauren Bishop, Michael Clark and Edward Phillips, met up after and celebrated by buying and drinking alcohol on the seafront.
CCTV from the Londis store nearby showed Phillips and Clarke laughing and joking shortly after carrying what the court heard was a brutal, vicious and horrific attack.
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Wiltshire Police are warning parents and children of stranger danger following reports of children being approached by strangers in cars.
Wednesday morning's weather for the west of the region
Wednesday morning's weather for the east of the region