Diana's husband Adam told ITV London that the public need to stand up and say "this isn't good enough."
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Karim and Guled have been missing from the Greenwich area for over a week and their families are concerned for their welfare.
Several areas of London will be illuminated over the next few days as a series of light installations take over the capital.
The Muslim convert is accused of encouraging acts of terrorism after posting a video on social media in September 2016, police said.