I always have this feeling that Zoro's childhood friend (that girl) was murdered…
How the hell does someone who fights day after day with real swords just fall off...the stairs...and...die...
Maybe later on Zoro will meet up with the killer and through that battle he'll complete his Tri Elements Sword.
Possible Suspect:
The girls dad xD...I just don't like the look on that girl's dad on the last page he was in... reminds of me the look of a dad that killed (well not killed, but did something else horrible) to his own daughter (Fullmetel Alchemist - forgot episode)
Either my theory was right or I dranked too many bottle of coke... <_<