User blog comment:FairyRaven/Fairy Tail Chapter 365: Fairy in the Jail!, Review and Commentary/@comment-4449950-20131230024638/@comment-24119374-20131231170255

On the "Natsu at Tartarus HQ" part: Don't forget Torafusa. Apparently, he was the one who killed Belno, if you think about it:

Ezel: Sliced the hell out of that city Jackal: KO and Possibly dead Sayla: Well, I don't need to say it... Franmalth, Kyouka, Silver, Keyes, Tempesta: Neither do I need to speak for them.

So, yep. Torafusa killed Belno and, judging by Gajeel and co.'s comments, he would make an excellent assassin.