The jury in the trial of Anxiang Du was told today that the businessman was unlikely to have been suffering from "severe depression" in the months leading up to the killings.
Giving evidence for the prosecution, forensic psychiatrist Dr Philip Joseph agreed with the defence that on the day Mr Du killed the Ding family, 29 April 2011, he was experiencing "some depressive symptoms", but said he doubted that Du had been suffering from "severe depression".
The court had heard that in the months before the killings, Anxiang Du had visited casinos and done shifts in his family's Chinese medicine shop.
This morning Dr Joseph said that in his clinical experience, someone with severe depression would typically be unable to function "to any effective degree", let alone socialise or work.
Rebecca Trowler QC, for the defence, argued in return that in some cases limited work would be possible:
She also told the court that Du had shown symptoms of depression at times since his teens, causing nightmares, sadness, and lack of sleep.
She recounted the death of his father, when Du was 16, saying after his arrest Du had told a psychologist it made things "all black, like a light had been put out.
Listening to this in court today, Anxiang Du hung his head in the dock and looked as though he was crying.
Dr Joseph argued that right up to the killings, Du had continued the legal fight against the Dings.
These did not seem, he said, the actions of someone who had given up, like a depressed person might do.
What is more, he said, after the killings Du seemed to follow a plan - not the behaviour, he thought, of someone who had lost control.
Anxiang Du admits killing Jeff, Helen, Xing and Alice Ding, but he denies four counts of murder.
The trial continues tomorrow.