Took searching up a few articles, but this one gave the most detail on how this was achieved.
It sounds like a mix of more modern detective and surveillance work, but all articles I read also mentioned a strong initiative to bring community involvement into the equation. Getting the nearby residents to pay attention and care more for the animals and to speak up to help the patrols seemed to be a constant theme in the official statements.
I'm happy they achieved such positive results. There was a proposal that did not pass to remove all the horns to deter poaching, which I feel conflicted about, and it's wonderful they were able to stop the poaching without resorting to that.