HONG KONG (REUTERS) - British investment banker Rurik Jutting was a narcissistic sexual sadist trying to cover a"fragile" shell after schoolboy abuse, according to his defence case against charges of murdering two Indonesian women in his Hong Kong apartment.

Opening Jutting's defence on Monday (Oct 31), lawyer Tim Owen called on Dr Richard Latham, a consulting forensic psychiatrist with Britain's National Health Service who has worked on between 50 to 75 similar cases.

Dr Latham told the Hong Kong court that Jutting suffered from recognised disorders from cocaine and alcohol abuse on top of his other personality disorders of sexual sadism and narcissism. He stated that at the time of the killings, Jutting's ability to control his behaviour was "substantially impaired".

"There is this very fragile sense of self esteem underneath it all," Dr Latham told the court, adding that Jutting's narcissistic tendencies of being boastful was a means to cover up.

Mr Owen said Jutting had been a victim of sexual assault during his teenager years at Winchester College, one of Britain's oldest and most prestigious public schools, when he was forced to perform oral sex on another boy. The defence also detailed Jutting's father attempted suicide when Jutting was 16.

Jutting, a Cambridge University graduate who previously worked at Bank of America Corp in Hong Kong, has been accused of murdering Sumarti Ningsih, 23, and Seneng Mujiasih 26, two years ago The women's bodies were found in his luxury high-rise Hong Kong apartment.

Ningsih's mutilated body was found in a suitcase on the balcony and Mujiasih's was found inside the apartment with wounds to her neck and buttocks, the prosecutor told the court.

Jutting has pleaded not guilty to murder on grounds of"diminished responsibility", but guilty to the lesser charge of manslaughter.

The trial has attracted international scrutiny since it began last week with media flying in from Britain to cover the case and the court room has been perpetually full.

Jutting captured hours of footage on his iPhone of him torturing Ningsih. He also filmed rambling monologues where he discussed the murders, binged on cocaine and explained his violent sexual fantasies.

"The thing I never had before in a case is the video recordings he made himself because they give you a direct view of what he was like around the time of these two killings,"Latham told the court.

Dr Latham said that in 2011, Jutting developed a strong preference for sexual violence, torture, rape and slavery. He moved from using pornography to "acting out these things with people in a consensual way and then he gradually testing out things that were not really consensual."

In 2013 Jutting started booking more submissive escorts and would opt not to use condoms, he said.

Jutting's alcohol abuse disorder was evident starting from 2011 and from 2012, things seemed to get more severe, Dr Latham said. At the time of the killing "it was at the most severe end of the spectrum", he said.

The prosecution team last week showed the court graphic and shocking footage of the killings. The video evidence also showed Jutting telling police he was consuming 10 packs of cocaine a day - each costing HK$1,000 (S$180) and that he ingested up to 20g of cocaine just before the second murder.

The defence and prosecution were largely in agreement over the physical evidence, but the dispute may lie in psychiatric and psychological evidence provided by the defence to determine whether it was a case of murder or manslaughter.

Murder carries a mandatory life sentence, while manslaughter carries a maximum of life though a shorter sentence can be set.

Dressed in a pale blue shirt, Jutting was clean shaven with short cut hair, looked attentive during the session. His loss of weight has been in stark contrast to initial court appearances when he looked heavily overweight and wore a thick dark beard.

Jutting, a former vice president and head of Structured Equity Finance & Trading (Asia) at Bank of America, had expressed "job depression" in his series of filmed monologues that he termed the "narcissistic ramblings of Rurik Jutting.