Legal Question in Criminal Law in Illinois

Interesting question. Normally, you would have no affirmative duty to report the criminal behavior of another person. In this case, however, given that the thief was your wife, there is a reasonable claim that can be brought that you were in receipt of stolen property (a possible criminal claim against you) or that you were unjustly enriched as a result of her conversion (one of a number of possible civil claims that could be brought against you). So long as you are married (the privilege against testifying against one's spouse ends, obviously, upon the dissolution of a marriage), the privilege against testifying against your spouse remains. That said, you would certainly be looking at liability that has nothing to do with incriminating your wife in a potential case against her.