A retired solicitor with a history of manic depression hanged himself after hospital staff failed to keep regular checks on him, an inquest heard.
Francis Bakewell, 74, was supposed to be observed every 15 minutes because of fears he may harm himself.
But he was left unchecked by hospital staff for more than an hour at the St Anne's Centre in The Ridge, St Leonards.
When it finally emerged Mr Bakewell was missing, the charge nurse found him hanged by his shoelaces behind a locked bathroom door.
Nursing assistant Valerie Pearce said she could not remember being told to carry out 15-minute observations.
St Anne's services manager Val Good told an inquest in Hastings an inquiry had been launched in the wake of the death, resulting in a series of changes to avoid a repeat of the tragedy.
The inquest heard Mr Bakewell, of Upper Maze Hill, St Leonards, had suffered mental health problems for years, leading him to be sectioned under the Mental Health Act.
He was admitted voluntarily to St Anne's in May, five months before his death on October 1 last year.
Mr Bakewell had spoken about committing suicide before. On one occasion he said: "It's all going to catch up with me - all the lies I've told all my life."
Mr Bakewell had been placed on round-the-clock observation up to two days before his death.
East Sussex coroner Alan Craze said if the observations had been carried out, Mr Bakewell may have been saved.
He added: "However, even a 15-minute observation of someone who intended to take his own life would not itself have prevented his death."
Mr Craze recorded a verdict of suicide.
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