Excuse the preamble,
Once yonks ago, here on the Gold Coast QLD close to YSPT, I heard a chopper flying around in circles. 9pm I went out and couldn't see anything but could hear it quite close and circling.
I was going nuts, saying to the wife, it's there somewhere, pointing to sky.....!
After about 5 minutes, I finally saw - the cockpit!
Yep, the glow from cockpit. No nav lights nothing. I couldn't believe it. And then I saw it again... No lights, black as night....
So I went to the local port and asked about it as we have the Sea World choppers based there and I assumed that this 'night' chopper might go there for refueling etc.
Back to the OP. Maybe find out the local ish airports or chopper bases and enquire there, or even ring them. If it's mossie stuff, then the local council would know.
Anyway, after my black night chopper enquiry, they rang me back and told me it was a police chopper and they - are - allowed to fly with no nav lights (so as the bad guys can't see them, LOL!).