By Farah Master

HONG KONG (Reuters) - A Hong Kong judge warned jurors that they will have to view video filmed by former British banker Rurik Jutting of the torture and vicious killing of two Indonesian women he is accused of murdering as the trial got under way on Monday.

Jutting, who studied at Cambridge University and Winchester College, one of Britain's most prestigious private schools, pleaded not guilty to murder on grounds of "diminished responsibility". He was arrested two years ago after the victims' bodies were found in his luxury high rise apartment.

The 31-year-old pleaded guilty to a lesser charge of manslaughter, and to a third charge of preventing lawful burial of a body.

During the jury selection, Deputy High Court Judge Michael Stuart-Moore warned potential jurors that if they were unable to cope with viewing extreme violence they should not take part.

"There is a particularly horrifying aspect of the case.

One of the victims was subject to extreme cruelty and violence," the judge said, explaining that a number of gruesome, and extreme color photographs could be presented during the trial.

“The defendant even recorded on his iPhone the torture inflicted on the first victim before she died."

Jutting filmed a series of videos including one showing the first killing, while in other videos he talks about his plans for the second, according to a court fact sheet.

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

Looking trim and dressed in a dark blue shirt, Jutting was clean shaven with short cut hair, in stark contrast to his initial court appearances when he looked heavily overweight and wore a thick dark beard.

The grisly nature of the case has cast a harsh light on the seamy side of Hong Kong, offering an insight into how some wealthy professionals binge on sex, drugs and alcohol.

Jutting who previously worked at Bank of America Corp in Hong Kong, was accused of murder in October 2014 after police found the bodies of Sumarti Ningsih, 23, and Seneng Mujiasih, 26, in his apartment. Both women's throats were slit.

Ningsih, who had a son in Indonesia, was visiting Hong Kong on a tourist visa. Her mutilated body was discovered inside a suitcase on Jutting's balcony, while Mujiasih, a domestic helper, was found lying inside with wounds to her neck and buttocks. She was working in a bar when she met Jutting, according to the fact sheet.

"HIGHLY GRAPHIC" VIDEO

Before the jury selection, Jutting's barrister Tim Owen explained the argument for diminished responsibility was based on the grounds of a personality disorder.

Prosecutor John Reading stated that psychopathic behavior was not a reason for diminished responsibility, setting up the arguments both parties will make during the trial.

Jutting was found fit to plea after undergoing psychiatric assessment at the end of 2014.

The jury has to decide if it is a case of murder, which carries a mandatory life sentence, or manslaughter, which carries a maximum of life though a shorter sentence can be set. On Tuesday, the jury will watch 30 minutes of "highly graphic" video. The public in the courtroom will not be able to see the video, though the sound will be audible.

The fact sheet said Ningsih was tortured for three days using Jutting's belt, sex toys, a pair of pliers and his fists. He eventually killed her in the bathroom, cutting her throat with a serrated-edged knife.

In video footage Jutting talked about watching porn including depicting violence and turning his fantasies into realities. He also talked about whether to turn himself in or hide the body and fly to Britain.

He called police to report the second murder. In a recording played in court Jutting sounded coherent, stating "obviously bad stuff has happened."

Investigators also found cocaine at his apartment, according to the fact sheet.

“I definitely could not have done that without cocaine,” it quoted Jutting saying.

Hong Kong, a former British colony, still retains a British legal system after being handed back to China in 1997.

The case is being closely watched by Hong Kong's 300,000-strong migrant domestic helpers community, many of whom come from Indonesia and the Philippines. Outside the High Court, about a dozen of their representatives held placards reading “Justice for Wanchai Murder Victim” and “Stop Violence”.

(Reporting by Farah Master, additional reporting by Venus Wu; Editing by Simon Cameron-Moore)