Even if he manages to find it, would it still be considered his property?

As far as I know, in most countries, whatever lands in the trash becomes property of the city/government. So even if he finds it, the governmetn could easily sue him and take it back? That would suck but for almost a billion USD, I imagine that would happen.

And what happens if someone else finds it first? Is it still considered his property, legally? He threw it away so he relinquished the ownership rights?