I don’t think revealing a source who is deceased in any way compromises the rest of his sources. If it is revealed that Seth Rich was giving him information and was killed, it will shine the light of truth on the democrats. This may serve to offer a small amount of protection to the other sources should their identity slip out.
Protecting the dems, if Rich was a source, is counter-productive to the whole Wikileaks mission.
I don’t think revealing a source who is deceased in any way compromises the rest of his sources.
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There are other considerations such as the impact on his family and close friends. It could put them in an uncomfortable position, if not some jeopardy. Assange has to think of their well being and respect their privacy.
That said, I agree with you it would shine a light on the truth.
Unless Seth Rich was working with another insider.