Police said the 24-year-old had travelled on the 2117 GMT train from Bickley to Penge East, crossed the footbridge over the railway to the Newlands Park exit en route to meet his friend.
Mr Guidera, an aspiring teacher who was studying history and politics at the University of Greenwich, had spent the day watching football on television with friends before getting the 21:17 GMT train from Bickley to Penge East, arriving just before 21:30 GMT.