The prime suspect in the death of New Zealand-born nurse Michelle Beets in Sydney last month has today been charged with her murder.

Walter Ciaran Marsh, a former colleague of Ms Beets at Royal North Shore Hospital, was arrested yesterday and this afternoon (5pm NZ time) was formally charged with her murder.

The 49-year-old United States national was to appear in the Hornsby Local Court later this evening.

Marsh had been interviewed twice previously in relation to the 57-year-old's death and last week took the extraordinary step of publicly declaring his innocence while forensic examiners spent three days searching his apartment.

He claimed he had been made a suspect because he was a foreigner and said he was meeting his wife at a railway station when Ms Beets was killed.

She died of multiple stab wounds to the chest, throat and head inflicted on the porch of her North Sydney home after returning home from a day shift in the hospital's emergency department about 6.20pm on April 27.

Police believe her assailant cut the power to her property and waited in the fading light to ambush her as she opened the front door.

Marsh's arrest ends a three-week investigation that focused on workmates who might have harboured a grudge against the popular nursing manager, who had worked at the hospital for 25 years.

She had interviewed Marsh for a position last year and sponsored his visa to live in Australia.

His contract with the hospital was not renewed after one year but Marsh denied any resentment towards Ms Beets.

When asked what he thought of Ms Beets last week he said: "I liked her, I was grateful .... I enjoyed the people I worked with and thought

"We all got along wonderfully."

On the evening Ms Beets was killed, two people walking their dogs saw a man wearing a green hooded jacket and backpack run from her front yard.

The man was later caught on security footage disposing of a backpack at a nearby shopping centre.

Marsh, in his public denial, said his dumping of a backpack in the mall was a coincidence.

Police subsequently searched through massive piles of rubbish at waste transit stations and dumps for items connected to the killing. The murder weapon has not yet been located.

Ms Beets was farewelled by more than 1000 mourners -- including family members from New Zealand and her partner David Grant -- at a funeral service in her home suburb of Chatswood on May 7.