To be able to catch the HTTP DELETE on a route you need to add
<remove name="UrlRoutingModule-4.0" /> <add name="UrlRoutingModule-4.0" type="System.Web.Routing.UrlRoutingModule" preCondition="" /> <!-- any other modules you want to run in MVC e.g. FormsAuthentication, Roles etc. -->
under system.webServer in Web.config