how to display 404 error from a template

Hi, How can I display 404 error from a template? I do

if( ! $bar->get_field('name') )
	{
		ob_end_clean();
		ob_start();
		$header  = 404;
		$text = get_status_header_desc( $header );

		$protocol = $_SERVER["SERVER_PROTOCOL"];
		if ( 'HTTP/1.1' != $protocol && 'HTTP/1.0' != $protocol )
		$protocol = 'HTTP/1.0';
		$status_header = "$protocol $header $text";
		echo $status_header;
		header("Location: http://www.example.com/");
		nocache_headers();
		include( get_404_template() );
		ob_end_flush();
		exit;
	}

but it throws 200 OK