Rurik Jutting needed a cocaine boost to give him the "courage" to brutally murder two Indonesian prostitutes but his "mental responsibility was not substantially impaired", a Hong Kong court heard.
In his closing statement at Hong Kong's High Court, prosecutor John Reading said the British banker had the capacity to form judgements and exercise self control before describing, in detail, how Jutting cut the neck of his first victim.
He cut the neck of Sumarti Ningsih, 23, as she knelt by a toilet bowl before dragging her into the bath to saw at her throat, eventually killing her.
He detailed Jutting's plans to torture his second victim – how he bought items including a hammer, blowtorch and pliers from a hardware store.
"Let's be clear about these, I am going to use these to torture someone in the most inhumane way possible," Reading said, reading out one of Jutting's statement in a self-filmed movie.
Jutting is accused of murdering Ningsih and his second victim, Seneng Mujiasih, 26, in a five day binge of drugs and violence at the end of October, 2014. Cambridge-educated Jutting denied murder on the grounds of diminished responsibility.
On Wednesday, the prosecution said that Jutting was in control of his actions at the time of the murders, phoning his mother after he killed his second victim.
His defence claims that Jutting's alcohol and cocaine addictions, and personality disorders meant that he was not in control of his actions at the time of the killings.
Defence lawyer Tim Owen said Jutting was not "asking for sympathy" and acknowledged he intended to kill both victims. However, he argued that Jutting had committed manslaughter owing to his diminished responsibility and inability to make rational decisions.
In Hong Kong, murder carries a mandatory life sentence, and manslaughter a maximum of life though a shorter sentence can be set.
His defence claims Jutting was under enormous pressure in his job as vice president and head of Structured Equity Finance and Trading (Asia) at Bank of America in Hong Kong, leading him to abuse alcohol and cocaine.
The judge is expected to sum up the case on Monday (7 November), with a verdict expected on 8 November).