Gosho didn't say unambiguously Eri is not the boss, so I haven't included her. She isn't even a good contender because it is unlikely the boss would give Gin permission to kill her own husband anyway.
Three out of four of the most suspected male characters have now been ruled out, leaving Atsushi left. Atsushi is already a bad pick because of how he behaved during Hidden Bathroom secret and because a character who married someone angelic like Elena is unlikely to order the deaths of his daughters.
There aren't many more major recurring characters introduced prior to the Kir arc full name interview who aren't ruled out by alibis like being with Haibara. I feel like Gosho is getting comfortable disclaiming these main characters because he isn't worried someone is going to name a character he can't deny. I get the feeling we should be looking a lot more minor, or even just for a background name.