The man accused of murdering a French student broke down six days after the killing and said he had taken an overdose, the Old Bailey has heard.
Levi Bellfield, 39, is accused of murdering Amelie Delagrange, 22, in Twickenham, South-west London in 2004.
The jury heard Mr Bellfield had become upset and told a friend: "You don't know what I have done".
The court was told he was taken to a mental health unit where he told staff he had overdosed on anti-depressants.
Mr Bellfield from West Drayton, west London, denies murdering Miss Delagrange.
The former wheel clamper and pub bouncer, also denies the murder of Marsha McDonnell, 19, two attempted murders and a kidnapping.
The prosecution allege he drove past buses and bus stops in various vehicles looking for young women to attack.
Miss Delagrange was battered over the head with a heavy object and found near a cricket square in Twickenham Green.
Brian Altman, prosecuting, said that six days after the death, Mr Bellfield's friend Richard Hughes found him in his bedroom.
"Bellfield was emotionally upset and needed help. He had been drinking," said Mr Altman.
Amelie Delagrange's parents have been in court for the trial
When Mr Hughes asked him what the matter was, Mr Bellfield allegedly replied: "You don't know what I have done", the court was told.
Mr Hughes took Mr Bellfield to Hillingdon Hospital and he was admitted to the mental health unit, Mr Altman told the court.
He said Mr Bellfield told staff he had overdosed on an anti-depressant the night before and that he had been feeling low and suicidal.
Mr Bellfield had left the hospital against doctors' advice the following day and had taken his family to Kent, the jury heard.
When Mr Bellfield's partner was later asked about his state of mind, she said he had been "down and crying all the time", the court heard.
The jury will spend Wednesday and Thursday visiting the various locations in west London, before hearing the rest of the opening of the case on Friday.