A 48-year-old American with a military background is being questioned by Sydney homicide detectives over the murder of New Zealand-born nurse Michelle Beets.

Ms Beets, 58, was fatally stabbed on the doorstep of her Chatswood home on April 27.

Walter Marsh, a former colleague of Ms Beets at Sydney's Royal North Shore Hospital, has been the main suspect in the case, the Sydney Morning Herald reported.

He was in handcuffs when he was escorted by police from his Lane Cove apartment about 6pm local time yesterday.

The newspaper said it was the third time the inquiry team had spoken with Marsh since Ms Beets' murder. Detectives had already devoted three days to searching his apartment.

A registered nurse, Marsh last week openly denied any link to the murder and said he had been made a target because he was a foreigner.

Marsh said Ms Beets had interviewed him for his job and sponsored his visa to come to Australia, where he had married and found happiness for the first time.

His contract with the hospital was not been renewed after one year, but he said this had not jeopardised his visa.

Ms Beets's brother, Marty Beets, said last night he had not been informed of any developments in the murder investigation.