I think both pilots should be/have been investigated. However, I think they are unlikely suspects and don't see the media asking about other possible suspects. I also think so much suspicion being put on the pilot to the point of claiming he committed a suicide/murder, especially at this point, is a not appropriate.... they've already even had the FBI look over his flight simulator and I'm not sure why any info was released on deleted files and such (then run with by the media). I delete files all the time. In general, I think they could look at other angles as I have mentioned regarding the pilot also.
But what about the passengers or crew or anyone who came in contact or had access to the airplane instead of being obsessed with the Captain to the exclusion of most else.