British banker Rurik Jutting who is accused of murdering two Indonesian women in his upscale Hong Kong apartment was a cocaine addict who had developed drug-induced fantasies, a court heard Wednesday.

   The 31-year-old Cambridge graduate and former securities trader for Bank of America-Merrill Lynch has pleaded "not guilty" to two murder charges, on the grounds of diminished responsibility.

   He pleaded guilty to manslaughter, which was rejected by the prosecution.

   Since the trial started Monday, jurors have viewed harrowing iPhone footage of Jutting torturing his first victim, Sumarti Ningsih, 23, for three days before he killed her by cutting her neck with a serrated knife at his apartment two years ago.

   Days later, he killed Seneng Mujiasih, 26, cutting her throat.

   Mujiasih's body was found in a pool of blood in Jutting's living room on November 1, 2014, while Ningsih's decaying body was discovered stuffed into a suitcase on his balcony.

   In court Wednesday, prosecutor John Reading said Jutting had become increasingly withdrawn and "deeply addicted to cocaine", citing a toxicologist's report.

   Footage from police interviews played in court showed Jutting saying he had started to take more cocaine at weekends for six weeks before the killings.

   "I've had cocaine previously, but not in such a large amount," he told police.

   "When I started taking it, it started bringing out long and extended fantasies," he said.

   Speaking calmly, he told police what he had done.

   "Yes I did kill her," he told two interviewing officers. "I cut her throat."

   "These are the only two people who have been killed by me," he added.

   Jutting told police that he had met Ningsih on the website Craigslist under the "casual encounters" section, storing her name in his phone as "Indo".

   He said that initially he had not planned to kill her.

   When asked by the interviewing officers why he had killed her, he replied:

   "It's a question which I think I'll always asks myself."

   He said he had considered flying back to see his parents in Britain before handing himself in.

   The jury was shown 20 photos recovered from Jutting's phone, including pictures of Ningsih bound and gagged, and of her body in the shower.

   Forensic pathologist Poon Wai-ming told the court Ningsih had been found in a suitcase in the foetal position, her neck severed.

   Jutting said that when it came to his second victim, Mujiasih, he had spent a few minutes deliberating whether to change his plan and not attack her.

   "For a period of time, a short period of time, the human side of me kicked in," Jutting said.

   "I did some more coke and that side of me just went," he added.

   Ambulance officer To Shing-fai described Jutting as talking to himself and crying in the hallway outside his apartment on the night the bodies were discovered.

   Jutting faces a life sentence if convicted of the murders.

   The killings shone a spotlight on the seedy underbelly of the finance hub.

Jutting's flat lay streets away from one of the city's red light districts. 

   Indonesian migrant organisations in Hong Kong have called for justice for the women, and compensation for their families. (AFP)