Pub chef Mark Dixie said: "I must have been mental do something like that, eh?" after his arrest in connection with the murder of Sally Anne Bowman, the Old Bailey heard.
Dixie, 37, denies killing the 18-year-old model but has admitted having sex with her dead body.
Sally Anne was stabbed seven times, including two major wounds that passed through her stomach and exited out the back.
Her body was found by a neighbour in Blenheim Crescent, South Croydon, on September 25, 2005.
The court heard Dixie was taken into custody at Sutton police station following his arrest at Ye Olde Six Bells pub in Horley on June 26, 2006, where he was working as a chef.
Before he was interviewed by detectives he was asked by the on-duty sergeant if he had any health problems or mental health issues.
In a statement to the court Sergeant Thornton said Dixie's reply was: "I must have been mental to have done something like that, eh?"
Dixie responded "no comment" to all the questions he was asked during his police interview, the jury was told.
The trial continues.
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