I would say wash it thru Monero and then mix it, from there if I were the illicit type I would try to do offline exchanges with gold bugs who are also crypto en

I would say wash it thru Monero and then mix it, from there if I were the illicit type I would try to do offline exchanges with gold bugs who are also crypto enthusiast to get it into hard assets. 1 Billion in gold is actually only about a half a semi-load full, it would take some time but assuming you fractured it into a bunch of different monero wallets, you have time on your side. If one get's compromised you take what you have and run. Because it would be safe to assume at that point that there are tools monitoring the chain by state level actors that none of us are privy to. If you are going to live that life paranoia is key.