Every day, Philip Nguyen's wife lights a candle in memory of slain Sydney police officer Constable William Crews, a court has heard.

Nguyen told the Supreme Court in Sydney on Friday he feels "extremely regretful and extremely sad" about the death of the trainee detective, who was shot dead during a drug raid at a basement carpark in Bankstown on September 8, 2010.

"I'm extremely remorseful and I wish to offer my apology to the family of the police officer William Crews and also to the police force," Nguyen, 57, said through an interpreter at his sentence hearing.

"I have asked my wife to light a candle for the officer ... on a daily basis.

"I have been feeling very sad about this whole incident."

Nguyen has pleaded guilty to manslaughter and to wounding Const Crews, 25, with intent to cause grievous bodily harm.

He did not fire the fatal shot but he was charged with manslaughter on the grounds of "excessive self-defence".

The court has been told Nguyen, a drug dealer, produced a firearm during the raid and fired it, hitting Const Crews in the arm.

The constable fired three shots in return before a fellow detective fired once, accidentally shooting him in the neck.

Nguyen's solicitor, Ho Ledinh, submitted that his client was remorseful and that his age and good prospects of rehabilitation should be taken into account when sentencing him.

But crown prosecutor Mark Tedeschi QC said Nguyen's apology "comes very late in the piece".

Even though Nguyen did not fire the fatal shot, the offence was still in the most serious category, he said.

Mr Tedeschi submitted Nguyen's assertions that he fired his gun because he felt threatened were contrary to the evidence.

"The fact he fired his weapon at such close range, the fact he hit a police officer in the arm, indicates more than an intention to scare people away," Mr Tedeschi said.

Const Crews' death was a "direct consequence of (Nguyen's) actions", the court heard.

The young policeman's parents were in court for Nguyen's apology.

They have previously described their devastation at the loss of their son, with his father, Kelvin Crews, telling the court, "There is no light at the end of tunnel."

Justice Elizabeth Fullerton said she believed Nguyen's apology was genuine.

"It seems to me it was a genuine reflection of his feelings," she said.

Nguyen will be sentenced next Friday.