There was in fact no rules broken here, if you did not see his warnings for the HS, then that is your fault and not his. Regarding the other situation, if you kill an innocent, no matter on why you killed them, you can be killed for it, even if you are proven, as soon as you kill an innocent you are instantly KOS'able, without the player even needing to question you.
If you do feel however that this was abuse, you can post a Report Abuse in this section and by following the template below
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[b]Staff Member(s) Name:[/b]
[b]Staff Member(s) SteamID:[/b]
[b]What Did The Staff Member(s) do?:[/b]
[b]What Server(s) Was This On?:[/b]
[b]Evidence:[/b]