London's top police officer, Commissioner Bernard Hogan-Howe, gave a lesson on the dangers of knife crime to teenagers at Edmonton County School - including the friends of a pupil who was killed last year.
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When you're trying to concentrate even the slightest sound can be a distraction.
The court heard how Roland McKoy killed his 22-month-old daughter Jahzara out of 'spite and resentment'.
Richard Deakin, the chief executive of NATS, was being grilled by MPs from the House of Commons Transport Committee.