A suspected suicide bomber was a driver and "dear brother" of extremist preacher Omar Bakri Mohammed, it has been claimed.
Abdul Waheed Majeed, 41, is suspected of being responsible for driving a lorry into a jail in Syria, Aleppo and detonating a bomb last week.
Officials have not confirmed the identity of the bomber.
It is thought to be the first time a Briton has staged a suicide attack in the war-torn state, where rising numbers of UK-born extremists have gone to fight.
Counter-terrorism officers have been searching Majeed's home in Martyrs Avenue in Langley Green, Crawley - the ex-home of murderer Roy Whiting.
Married father-of-three Majeed, known as Waheed, left Britain six months ago, telling his family he was going on a humanitarian mission to Syria.
Speaking from his flat in Tripoli, Bakri described Majeed as "a very dear brother".
He claimed Majeed had been an active student and valued member of the banned extremist Al-Muhajiroun organisation between 1996 and 2004 and was someone who wanted to further the "Muslim cause".
Bakri said Majeed would organise his sermons in Crawley and record the lectures and distribute them.
He said: "He was a good brother. He was someone who was always at hand to help people.
"He wanted to study Islam and wanted to know what it was to be a good Muslim. He was also very interested in the issue of how we could establish an Islamic state."
Tensions in the Crawley Muslim community is high over the issue.
Chief Inspector Justina Beeken said: "The inquiries by the South East Counter Terrorism Unit are ongoing and we are closely liaising with them and the community in the town. There has been no formal identification of the man and therefore we cannot confirm who he is or where he is from.
"There has been a lot of media and social media coverage around Syria and we are working with the local community to reassure and engage with them regarding this. We are a community which always pulls together and supports each other.
"We all collectively condemn any acts of terrorism and continue to offer our sympathies to all those affected by the crisis in Syria."