Run Server Side Function On Dynamic HTML Control?

I am trying to create an HTML button that can use a C# server side delete function. since I don't know how many results I will have at the page, the control is created dynamically when the end user searches for current Messages:

CmsContactUsContent += string.Format("
"<input type='image' value='delete' id='del{8}' runat='server' onClick='DeleteItem' img src='/MaromyDotNet/img/AdminIcons/note.png' style='width:16px;'/>" +
"</div>" +
"<div style='clear:both'></div></div>", message.ContactMessageId);

There is a Class called ContactMessage and I'd like at each iteraion to allow the user to delete the current message through this function:

public void DeleteItem(object sender, EventArgs e)
{
int idToDelete = 41;
BLLContactMessage.deleteMessageById(idToDelete);
}

However, the event does not fire.