How do I find the killed person's name?

I'm trying to show a gui that says that a player killed someone. I'm having trouble finding out the player's name and when they kill someone.

local gui = script.Parent
local plr = game.Players.Localplayer

--I don't know how to do this, but I'm trying to find if they killed someone.
    gui:Clone().Parent = plr.PlayerGui
    gui.TextLabel.Text = "You killed "..deadperson.Name --"deadperson" would be the player who died. I don't know how to figure out when the player killed someone and how to find the deadperson's name.
end