President Obama has nominated John Brennan to be the new director of the CIA, replacing David Petraeus who resigned over an extramarital affair.
Brennan is a controversial choice for Obama after questions have been raised about his views on enhanced interrogation techniques used on terrorism suspects during the Bush administration.
The appointment must still be confirmed by the Senate.
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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."