A couple campaigning to discover how their son died in an accident at Oxford station say a report given to them was "censored".
Ecologist Adrian Fowler, 29, was killed in August 1995 when he fell from a train at the railway station.
Sissel Fowler, 63, of Squitchey Lane, north Oxford, and her husband Godfrey, 73, have been repeatedly told they cannot see a Thames Trains inquiry report, which was circulated within the industry.
Mr and Mrs Fowler The couple hoped new freedom of information legislation would help them find out more.
A two-page summary of the report's conclusions has been issued to them by the Health and Safety Executive -- but crucial witness statements from 10 rail staff who gave evidence to an internal inquiry have been excluded.
Mrs Fowler said: "I find it extraordinary that someone can be killed in a public place and witnesses are allowed to keep secret what they said about it.
"Some material has been deleted so we cannot read it, which is very frustrating."
Prof Fowler added: "The summary concludes that Adrian was late for the train and tried to get on it but it is not clear if the train was stationary or moving off at the time.
"The HSE's freedom of information officer says they cannot release the witness statements, even if their names are not revealed because it would breach the Data Protection Act.
"We have a situation where you try to use one piece of legislation, the Freedom of Information Act, to get certain information, and then another piece of legislation is quoted to deny you that.
"We have not had full disclosure of the information we need and we will give the HSE a short amount of time to approach the witnesses to see if they will give permission for their statements to be released.
"If that is not successful we will then appeal to the Freedom of Information commissioner."
Adrian suffered fatal head injuries trying to board the train on his way to a job interview in Scotland. There was a full inquiry into his death, but the Fowlers say the witness statements would provide them with vital information about central locking mechanisms for train doors and the position of the senior conductor on the day of the tragedy.
HSE spokesman Karen Eldridge said: "We need to seek consent from those interviewed to disclose evidence and we are seeking permission, although we rely on help from other organisations to trace the witnesses.
"Following the Freedom of Information Act we were able to release this partial report and will continue to try to take this forward for the Fowlers."
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