What Is the Criminal Investigation Division of the IRS? Well the Criminal Investigative Division is exactly what it sounds like it is the central investigative body charged with investigating and building cases against people who are charged with tax crimes so Criminal Investigation works with a variety of different agencies to help build up the tax side of a case so for example they can work with the FBI they can work with Homeland Security they can work with a variety of different agencies to help build and prosecute those who cheat on their taxes now the reality of the situation is is the Criminal Investigation Division is a very small unit but they're a very focused unit so the way that the government sends a message to tax criminals is with a very high conviction rate and currently the US Attorney's Office when it comes to tax crimes enjoys a 90 percent conviction rate that's pretty staggering and the reason they're able to enjoy that that big of a convict conviction rate is because of the work that the Criminal Investigation Division does Criminal Investigative cases often take a very very long time to develop but once they do they're very focused they've usually got the people in their sights dead to rights and they're very thorough investigations so that's what the criminal investigative unit is that's what it does and that's why you should be concerned about when they're involved in your mouth.