Injecting Table Row Inside Repeater Item

I am trying to inject inside repeaters items, the problem is that the row is generated in a wrong location. If you try this simple example, you will see that the rown is generated under label '2' as it should be generated under label '1'. Why does it happen? And how to fix that?

protected void Page_Load(object sender, EventArgs e)
{
int [] array = {1,2,3,4,5};
rpt.DataSource = array;
rpt.DataBind();
}
protected string _extraRowHtml;
protected void rpt_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
if (e.Item.ItemType == ListItemType.Item ||
e.Item.ItemType == ListItemType.AlternatingItem)
{
int tmp = ((int)e.Item.DataItem);
_extraRowHtml = tmp == 1 ? "<tr><td class="topicsRow" colspan="100%"> Topics </td></tr>" : string.Empty; ;
}
}
<asp:Repeater ID="rpt" runat="server" onitemdatabound="rpt_ItemDataBound">
<HeaderTemplate>
<table cellpadding="0px" cellspacing="0">
</HeaderTemplate>
<ItemTemplate>
<tr style="height:50px">
<td>
<asp:HyperLink ID="lnkTitle" runat="server" Text='<%# Container.DataItem%>'/>
</td>
</tr>
<%# _extraRowHtml %>
</ItemTemplate>
<FooterTempl
</table>
</FooterTemplate>
</asp:Repeater>