Your question is really good. To put it simple our Nigeria government has their own personal business with Bitcoin. And I'm sure if dey do confiscate some Bitcoin from criminals they won't say because they know that they can actually use it for their own purposes.
However, the government finds it difficult to control Bitcoin technology because it is not under any centralised authority which leaves them in the dark. Given that they lack clear laws to deal with it and also lack the advanced skills and technology to track down and confiscate these criminals. because of that it has become a challenge for them So for me the probability of finding these criminals is very low.