A man convicted over the killing of NSW Police accountant Curtis Cheng has recanted his apology to the victim's widow because he "slipped up" and actually isn't remorseful, a Sydney court has heard.

Milad Atai, who was convicted for aiding the boy behind the 2015 shooting, apologised during a sentencing hearing for the hurt he put Selina Cheng and her family through.

But on Thursday, the NSW Supreme Court was told he had since written letters to federal police and a crown prosecutor saying those apologies made in September weren't truthful and he only said them "because I was in the heat of moment and I just slipped up".

More to come

AAP