ASP.NET MVC - HttpException or return view?

I'm trying to make a request for a customer and if the customer doesn't exist it should return some kind of "Not found" page. Which of the below would be the best practice to use for such a task, and why?

public ActionResult Index(int id)
{
    if (customerService.GetCustomerById(id) == null)
        return View("NotFound");

    return View();
}

or

public ActionResult Index(int id)
{
    if (customerService.GetCustomerById(id) == null)
        throw new HttpException(404, "Customer not found");

    return View();
}