George Paul witnessed the arrest of one of the suspects in Westborne Grove and told ITV News he saw "three policemen holding down one individual - I don't know what ethnic origin he was but he was shouting.
"It was all over in ten minutes."
More top news
At least 2,400 cancer sufferers die needlessly every year because their GP does not refer them to a specialist quickly enough.
It comes after shadow chancellor John McDonnell made a surprise U-turn on the Tory budget vote which is due later today.
Georgia Williams could have been saved if police had not missed several chances to catch her killer, a review found.