In February, when the Herald broke news of the burglaries, Prime Minister Jacinda Ardern said she would be "taking stock and taking action" if foreign actors were responsible.
But in Wellington yesterday she sought to draw a line under the matter.
"I said if there was any instance or evidence found of foreign interference, then it would be up to us to act on that. The advice I have seen has been that has not been the case," she said.
Intelligence analyst and former University of Auckland lecturer Paul Buchanan said the Brady investigation - alongside whether Huawei equipment should be banned over security concerns - posed major risks of seriously rupturing the China-New Zealand relationship.
He said the announcement by police defused - for now - that risk, but raised additional questions.
"It's amazingly diplomatic, or cowardly, depending on which way you want to look at it," he said.
"You go almost for a year, in investigating this, and at the end you say you have nothing? Basic questions of competence begin to be raised."
The Herald has obtained a letter sent to Brady by police on February 19 which said the burglary had been ruled a low-value crime and had been closed. "We can't proceed any further with this case," the letter said.
Veteran private investigator Ron McQuilter said evidence, particularly forensic, needed to be gathered quickly and before a crime scene became stale or disturbed.
"The longer the delay, the more chance you've got of losing and chance to investigate it," he said.
McQuilter said he had never heard of a burglary investigation stretching for a year. "You can safely say this hasn't been treated as a normal domestic burglary - as I'm sure most people who have been burgled could tell you."
Police yesterday refused to make available the officer in charge of the investigation, or indeed anyone, for interview. Their comment to date on the case has been limited to a handful of short written statements.
A spokeperson for police said the February 19 letter was "sent in error, and this is regretted" (an explanation not provided last year when the Herald first asked questions about the document) and rejected the suggestion their investigation had been hamstrung by delays.
"We are satisfied that every forensic opportunity in relation to the investigation has been thoroughly explored and there has been no delay in the gathering of forensic evidence."
Buchanan said while the police had been unable to reach conclusions in the case, the New Zealand Security and Intelligence Service may have reached some of its own.
"If suspicions were raised it was agents of the Chinese state - that's an NZSIS counterintelligence job. That's, pure and simple, what they're supposed to do."
A spokesperson for the NZSIS declined to address their role in the Brady investigation. The Herald has previously reported their involvement in the case, including having swept Brady's home and office for bugs.
"The NZSIS has a long-standing practice of not commenting on what may or may not be operational issues," the spokesperson said.
Questioned more generally about whether New Zealand individuals and institutions were subjected to foreign interference, Rebecca Kitteridge, the director-general of security said in a statement: "New Zealand, like many other countries in the world, is the target of foreign interference activity. Preventing and detecting this sort of activity is a high priority for NZSIS."
-Additional reporting by Derek Cheng
