I got the same call a couple of days ago from "Michael Delgado of Crime Investigation Division of the IRS" and the message was very similar to what you stated.  I wasn't sure if it was legitimate or a scam.  I was panicking.  Glad I found this forum.  The phone number that he left was different than the one you mentioned, but I was unable to capture all of it from the voice message because it had cut out.   I'm sure he's changing his call back number since it's been a year ago since he started doing this.