How can I get a player's character and humanoid from a server-side script?

I've searched through so many devforum posts yet I have not found an answer. I need to find the character to get the humanoid so when a player activates an admin command to kill a player, the player stated is killed. Here's my script.

Once again, it's a server script.

commands.kill = function(sender, arguments)

    print("Kill command fired by "..sender.Name)
    local plrToKill = arguments[1]
    if plrToKill == "me" then
        plrToKill = string.lower(sender.Name)
        arguments[1] = plrToKill
    end
    local plrChar = game.Workspace:FindFirstChild(plrToKill)

    if plrToKill then
        local plr = findPlayer(plrToKill)

        if plr then
            local plrHum = nil
            local health = nil
            print(plrChar)

            plrHum = plrChar.Humanoid
            print(plrHum)

            health = plrHum.Health

            print(health)

            health = health - 100
        end
    end
end

Everything else works fine, but I get an error saying "attempt to index nil with 'Humanoid' which I find very confusing. Any help is greatly appreciated.