The man who died after he was struck by an oncoming train at Wandsworth Common has been named as Simon Brown.
The 24-year-old from East Grinstead was killed on Sunday afternoon when he lowered the window of the Gatwick Express train he was on and looked outside.
On a justgiving page, set up to raise money for his funeral costs and headstone, family friend Reuben Smith said: "Simon was a great friend of ours and a real light in the railway world.
"He was always smiling cheerful and would bend over backwards to help anyone.
"There's now a massive hole in our close knit community where he was.
"He has been taken from us at the age of 24 it's far too young.
"Please donate. I want to have this memorial train in his coach that he spent hours on and I want to help ease the burden of the cost of the funeral for his parents having had to bury my younger brother 11 months ago I know how hard it is."
On Monday, a British Transport Police spokesman said: "The man sustained serious head injuries on board a Gatwick Express train travelling to Victoria from Gatwick at around 5.30pm.
"Ambulance crews attended the scene but despite their best efforts, he sadly died a short time later.
"The death is being treated as non-suspicious and the circumstances, including what caused the head injuries, are still being investigated."
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