I live in NZ. At this point in time they haven’t reported anything conclusive about the index case for the Auckland Cluster.
What they do know is that the genome for this cluster is not one present in other cases previously caught at the border.
One of the working theories was that it came in via the cool store, but they haven’t been able to prove that theory.
There’s been no reporting that I’ve seen about importing the virus via illegal sea crossings between NZ and Australia (the Tasman Sea is pretty wild at this time of year), or via someone working in duty free at the airport.
For the later case you’d have to assume that the person gave two false negative tests at Day 3 and Day 12 of managed isolation, otherwise they would have been able to trace it. Alternatively, it would have needed to be a transit passenger and not subject to our managed isolation scheme.
The case of the hotel maintenance worker is different again. The virus genomes are different and have been linked to an elevator ride at the hotel. This is despite cleaning and PPE and distancing, so it gives a good indication of how sneaky this virus can be.
There is a full breakdown of data on our Ministry of Health website.