They haven't been caught because they are not located in the US. These calls originate overseas using the internet and VoIP phone services to try and run their scams.
I also received the same type of message about the "United States Treasury", and I needed to call to avoid appearing before a "magistrate" or "grand jury". I tried calling back but there was no answer, no voicemail.
This is the third time in a few months I have gotten a call like this. I laughed my [***] off as I listened to the message they left, using a very official tone of voice:
"Hi. My name is David Gray and this message is intended to contact you regarding an enforcement action executed by the United States Treasury intending your serious attention. Ignoring this will be an intentional second attempt to <unintelligible> your appearance before a magistrate judge or a Grand Jury for a federal criminal offense. My number is 302-569-3017. I repeat, it's 302-569-3017. I'd like you to cooperate with us, and help us to help you. Thank you."
I got the exact same message. I did call the number back (I knew it was a scam) and acted clueless. The fellow told me that agents were on their way to my home to arrest me and that I HAD to give them information ASAP or face arrest. I suggested that they contact my accountant (which shut them up), then stopped playing. I let the dude know that I knew this was a scam and would report them if they bothered me again.