asp:Button CommandName as Async Trigger for UpdatePanel

I am trying to capture the CommandName from button click events. I have at the top of the form my script manager

<asp:ScriptManager ID="scriptManager" runat="server"></asp:ScriptManager>

Then I have four buttons and they trigger an update panel

            <div class="grid-toolbar">
            <div class="tb-title">"Colorful Report"</div>
            <div class="tb-commands">
                <div class="left">

                    <asp:Button ID="btnSummary" CssClass="TabButton" UseSubmitBehavior="true" CommandName="Summary" runat="server" Text="Summary" ClientIDMode="Static"></asp:Button>
                    <asp:Button ID="btnExceptions" CssClass="TabButton" UseSubmitBehavior="true" CommandName="Exceptions" runat="server" Text="Entry Exceptions" ClientIDMode="Static"></asp:Button>
                    <asp:Button ID="btnOverdue" CssClass="TabButton" UseSubmitBehavior="true" CommandName="Overdue" runat="server" Text="Overdue Completions" ClientIDMode="Static"></asp:Button>
                    <asp:Button ID="btnInfo" CssClass="TabButton" UseSubmitBehavior="true" CommandName="Info" runat="server" Text="Info" ClientIDMode="Static"></asp:Button>

                </div>
            </div>
        </div>
        <div id="dataWrapper" style="overflow-y: auto; height: 600px;">
            <asp:UpdatePanel ID="panelGridView" runat="server" UpdateMode="Conditional" ClientIDMode="Static">
                <Triggers>
                    <asp:AsyncPostBackTrigger ControlID="btnSummary" EventName="Click" />
                    <asp:AsyncPostBackTrigger ControlID="btnExceptions" EventName="Click" />
                    <asp:AsyncPostBackTrigger ControlID="btnOverdue" EventName="Click" />
                    <asp:AsyncPostBackTrigger ControlID="btnInfo" EventName="Click" />
                </Triggers>
                <ContentTemplate>

                    <asp:TextBox ID="txtInfo" runat="server" TextMode="MultiLine" Width="400px" Height="200px"></asp:TextBox>

                </ContentTemplate>
            </asp:UpdatePanel>
        </div>

I then set the event in Page_Init

        protected void Page_Init(object sender, EventArgs e)
    {
        try
        {
            raMetaData.Initialize(HttpContext.Current.Request);
            btnSummary.Click += btnTabClick;
            btnExceptions.Click += btnTabClick;
            btnOverdue.Click += btnTabClick;
            btnInfo.Click += btnTabClick;
        }
        catch(Exception ex)
        {

            messages.Error("An error occurred while initializing page. Please try again.");
            Logger.Write(MessageType.Exception, ex.ToString());
        }
    }

But I can't figure out how to get the CommandEventArgs that e.CommandName is part of. e.CommandName is not part of normal EventArgs.

        private void btnTabClick(object sender, EventArgs e)
    {

        //string cmd = e.CommandName;
        string cmd = "?";

        switch(cmd)
        {
            case "Summary":
                txtInfo.Text = "This will be summary data";
                break;
            case "Exceptions":
                txtInfo.Text = "This will be exception data";
                break;
            case "Overdue":
                txtInfo.Text = "This will be overdue data";
                break;
            case "Info":
                txtInfo.Text = "This will be info data";
                break;
            default:
                break;

        }

    }

What am I missing?