What are the laws?

If a vehicle is stolen, and then sold, and the police know where the vehicle currently is and who has it, what would be stopping them from going and getting it?

Bit of a back story:

My brothers 2008 hilux was stolen in October last year, the person who stole it, sold it the same day. The police have said they have located the ute, and have been in contact with the person who has it in their possession and knows where he lives ect (innocent buyer). The police have told my brother, they need to contact the person who stole it, but it’s been months and they haven’t got in contact with the thief, so my brother is still at around a 18k loss as it had no wof or reg so no insurance either.

What I don’t understand is why they need to talk to the thief? It is marked stolen on the nz police website, so why can’t they just seize it and return it to original owner (my brother) also isn’t it illegal to purchase/receive stolen goods? So the person who has it, should have it taken off him?

Just wanting some advice from someone who knows their stuff about the law, because going off what I’ve read, the police aren’t doing what they should be doing…

Thanks 🙏