Fiona Spargo-Mabbs gave her son a kiss and a hug, and told him she loved him. Daniel responded by saying "I promise I won't die" before leaving the house and heading to a rave where he collapsed.
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Police have released an e-fit of a man suspected of attacking her.
The force has been tweeting after carrying out a series of dawn raids.
Adenike Akingbogun made the dangerous manoeuvre after ignoring the crossing lights and driving onto the tracks.