Paul Taylor, was described as a "sexual predator", has been found guilty at Chelmsford Crown Court of the 1979 murder of Sally McGrath, 22, from Peterborough, and five attacks on other women.
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Armed officers will be on patrol at major infrastructure sites across Essex and the county will see more police patrols.
The major party leaders' campaigns for the General Election will remain suspended on Wednesday following the Manchester terror attack.
Counter-terror police have arrested a man at Stansted Airport on suspicion he planned on travelling to Syria.