Footage has emerged which appears to show a truck, apparently driven by Abdul Waheed Majeed on his way to carry out a suicide attack in Aleppo.
Majeed 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.
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The Metropolitan Police Federation, which set up the official JustGiving site, said it felt a "suitable amount" had been collected.
There is no evidence the Westminster attacker Khalid Masood was associated with so-called Islamic State or al Qaeda, the Met Police said.
Janet Ajao said in a statement: "I do not condone his actions nor support the beliefs he held that led to him committing this atrocity."