Hertfordshire police are baffled by the mysterious death of a 13-year-old girl whose body was found with no shoes on below a railway bridge in Berkhamsted.

Zoe Miller, 13, regarded as a "perfect daughter" by her parents, was described as adventurous and with an unstoppable zest for life.

Police believe the teenager went out early for a walk, left the back garden of her family home and strolled barefoot on to the road behind it.

They also believe that she sat on top of the railing where, just below, was a train track. Police are working on a theory that she was startled by a train rushing past and she fell to her death.

DI Andy Rose of British Transport Police said: "We are determined to work out exactly what happened to Zoe and I am calling on people who may have been in the area to help.

"Zoe has left behind a distraught family and we want to be able to tell them exactly what happened and help them come to terms with the tragedy."

The family told the Daily Mail: "Zoe was an adventurous, brilliant, creative, beautiful, happy and wonderful daughter."

Her mother, Jane, said: "She was an incredibly bright and thoughtful person, always with a book nearby, often quiet and shy; also energetic and adventurous and often with views beyond her age."

"We're all in complete shock, she had everything to live for. That's why we think this was a tragic accident.

"She always used to climb trees while she was growing up and was a keen mountain climber. I think she climbed on to the footbridge and was watching the world go by when she somehow fell.

"There's nothing to say it was suicide. She left no note and had laid out her school uniform.

"We think that she was just messing around and did not perceive what would happen."