untested

Code:
<?php

if(!empty($_GET['file_id']) {
    
    // do any additional stuff
    
    switch ($_GET['file_id']) {
    case 0:
       header("Location: http://fileLocation.com");
       break;
    case 1:
       header("Location: http://fileLocation.com");
       break;
    case 2:
       header("Location: http://fileLocation.com");
       break;
    default:
       echo "No file found with that id";
    }
    
    exit();
    
} else {
    echo "Please specify a file ID";
}

?>