Caroline, 13, died while on a trip to Pleine Fougeres in Brittany with 40 pupils from Launceston Community College. She was sleeping on a mattress on the floor of a room with four other girls on 18 July 1996.
Her mother, Sue Dickinson, 41, from Launceston, is claiming damages against the education authority, Cornwall County Council, for negligence and breach of duty. She could receive pounds 22,578.
Mrs Dickinson's counsel, Stephen Killalea, yesterday referred the High Court, sitting in Plymouth, to the evidence of Jacqueline Thorpe, a teacher.
Mrs Thorpe said that at 3.55am she went to the lavatory and went back to bed. She immediately heard footsteps outside, got up, listened for five minutes then went back to bed.
"Just before 5am I woke again, hearing the same footsteps outside," she said. She went to the window and saw a man walking from the hostel to the main road. He did not appear to be acting furtively.
Mr Killalea told the court: "The likelihood is that man was the murderer ... The obvious inference is that was a man who went in the front door about 4am and came out from the front door about 5am."
The front and rear doors of the hostel were not locked.
Mr Killalea said that the teachers on the trip had a duty of care towards the children.
Earlier, Tim Kerr, for the county council, said the investigations, planning, execution and arrangements for the tripwere competent, diligent and meticulous. It was not incumbent on county council employees to see if the doors of the hostel were locked, adding that the attack on Caroline was not a foreseeable consequence of the negligence alleged.
Mr Justice Steel said he would give judgment in Exeter on a date to be fixed. It was a "sensitive and difficult decision" that required, and deserved, mature thought.