I need to dig out issue one and re-read it again, but after re-reading issue six today, I still think Ray's the killer.
On the last two pages where we see Jean and Ray discussing Sue's murder, Ray is in the other room, Jean can't see him, and he has the most malevolent grin on his face. Either Rags really screwed up drawing Ray's facial features (conveying evil glee when he meant to convey something else) or Ray is gloating over having murdered Sue and having gotten away with it.
That doesn't mean the stolen technology isn't somehow tied into it (I still think Ray's patents have something to do with this story) but Ray looks guilty as hell.
