Could someone please explain the grammar in the following sentence? I'm particularly interested in the を解決中だ portion.
I suspect that this might be a set grammatical pattern because it seemingly disobeys two that I am aware of. I am under the impression that ながら can only be used to describe two simultaneous actions (where the first is assigned a higher priority in the mind of the speaker). This sentence seems to be using it with だ. Further, there doesn't seem to be a verb that 難事件を could be the object of.
My best guess is that 解決中だ is an alternate way of expressing 解決している or something like that.