Curtis Cheng, 58, a police accountant, was shot from behind as he walked away from NSW Police headquarters in Parramatta on October 2 last year.

Selina Cheng told Nine News on Monday that she felt immense guilt after the tragedy, as her husband had almost left work early that day.

Mr Cheng had offered to take his wife to see the doctor, but in the end she didn't need to make an appointment.

She could not have known that her husband leaving work at his usual time would put him on a collision course with radicalised 15-year-old Farhad Jabar.

"Was it fate? ... I don't know," Mrs Cheng said.

"I was so guilty. I was very guilty. I thought I give my husband more time at work. He wanted to look after my health, but he didn't take off and the tragedy happened."

In the months following her husband's death, she constantly questioned why he went to work and didn't come back.

"I don't want anyone to suffer like me, as a widow," she said.

Mrs Cheng said she fell into "total despair" after her husband was killed, and felt that she was living in darkness. Then, as she was supported by police officers, victims' support groups and friends, a "beam of light" made its way into her life.

"Without those people I don't think I can be able to walk on," she said. "I know they will be beside me to continue the journey in life."

Seconds after her husband was shot dead, his killer was also fatally shot by one of several special constables who were protecting the building.

Mrs Cheng said she has met with the man who shot Jabar, and the pair had "a big hug" and cried together when she said she understood that he wasn't able to save her husband.

"You saved the rest, you saved more people," she recalled.

"I remember, I really remember that moment. Both of us just burst into tears."

As NSW Police plan to rename the Parramatta building where he died after Mr Cheng, Mrs Cheng said her "inspirational" husband will always have an impact on the lives of his family.

The inscription on his grave reads: "Your kindness, gentleness and patience will continue to guide us".