The IRS has this ingrained thing about contacting you first by US Mail. If it's escalated to a warrant, with Sheriffs and flashing lights and drawn guns out on the front lawn, and fathers led away shamefully in handcuffs before the tearful eyes of their own children, you've already gotten several very impressive-looking pieces of mail and already know full well that you're a criminal in the eyes of the law. It won't come as a surprise phone call on a Thursday morning. While it's possible that all those previous snail-mail contacts were filched by the neighbor's 10-year-old delinquent and you never saw them, that's doubtful. I've received several of these calls and they all left messages. I've kept the messages. Two were from the same guy (same voice) six months apart, using different names -- names not usually associated with his strong ethnic accent. (Kevin O'Connor is probably not a lifelong resident of Bangalore.) While this particular call did not leave a message, I can guess from the other posts the kind of message that might otherwise have been left. I call scam.
>> why can't you go after this criminal threatening people for money? <<
Because
1) We are not Law Enforcement
2) We do not have the authority
3) The IRS scammers are probably in India or Pakistan, and that is a long trip
4) YOU have not identified who are the criminals
5) YOU have not given us their names, addresses, and other important information
6) YOU have not read the many warnings about this scam
7) You will probably not return here to read the answers, and help find the real scammers.