In Volume 21, Chapter 190, Mr. 1 mentions that Zoro killed a previous Mr. 7 sometime before he met Luffy. http://www.onemanga.com/One_Piece/190/07/
In Volume 36, in an SBS, Oda drew a crude drawing of the first Mr. 7 Zoro apparently killed. Even for a crude drawing, he shares a lot of similar...
