Warren Francis Rogers, 70, has pleaded not guilty to the murder but guilty to the manslaughter of his wife of four decades, Anne Rogers, in their Milperra home in September 2016.

In the NSW Supreme Court on Wednesday, crown prosecutor Nanette Williams called forensic psychiatrist Dr Adam Martin to give evidence about his interview with Rogers in custody in August 2017.

Rogers and his wife separated for several weeks in mid-2016 but he asked her to return "when he was unhappy" being alone, on the condition she have no further contact with Jeff Langham, Ms Williams has previously said.

Mr Langham last week gave evidence he caught the train with Ms Rogers when they were teenagers, and reconnected when she sent him a Facebook friend request in 2013.

Reminiscing about childhood lead to them chatting "every second day" on various social platforms, he said.

During their two-hour interview, Dr Martin said the accused had recounted Ms Rogers "would spend a lot of time on the computer upstairs" and "she would delete the screen when she heard him coming".

Rogers said his wife, in July, had "sworn on her mother's grave she wouldn't contact" Mr Langham anymore, so he became "cranky" when she confessed that she still was, in September, and he pinned her arms to the bed.

He allegedly told her: "How can you do this? You've broken my heart, wrecked our marriage, destroyed the kids".

Rogers told Dr Martin his wife kicked him twice in the shoulder and head, and one of his teeth broke.

"The kick to the head was what set me off," he is said to have told the psychiatrist, before allegedly admitting to smothering Ms Rogers with a pillow.

Dr Martin said Rogers denied having planned to kill his wife and said he "planned to plead guilty to manslaughter because it wasn't premeditated".

Defence barrister Richard Pontello has asked the jury to consider the defence of substantial impairment by abnormality of mind, as Rogers became "very depressed" after learning of the extramarital relationship.

The court heard Rogers spent the day of the alleged murder shopping with his wife, talking to his daughter on the phone, and also went for a swim.

Dr Martin said he is "not confident" the accused was suffering from a major depressive disorder at the time.

"My view is that the actions were deliberate and purposeful," he said.

"I don't think there's much evidence to say that he completely lost control.

"I think the question for the court is the degree of how impaired he was."

The trial continues before Justice Julia Lonergan.

Australian Associated Press