Counter-terrorism teams are searching a property in Crawley amid claims that a Briton staged a suicide bomb attack on a prison in Syria.
Officers are examining a house in Martyrs Avenue in Langley Green after reports that a UK jihadi, who used the name Abu Suleiman al-Britani, carried out the deadly bombing.
He is said to have driven a lorry into a jail in Aleppo and detonated a bomb last week, and is thought to be the first Briton to stage a suicide attack in the war-torn state, where increasing numbers of UK-born extremists have gone to fight.
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Calum McSwiggan posted a photo on Instagram as he lay in a hospital bed after the alleged attack.
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