The legal scholar blog Volokh Conspiracy:

So says a County Attorney’s declaration filed on May 22, 2012 in a federal case challenging the polygamy ban on constitutional grounds:

The policy, as officially adopted by the ... County Attorney’s Office, states:

Prosecution of Bigamy Crimes:
The ... County Attorney’s Office will prosecute the crime of bigamy ... in two circumstances: (1) When a victim is induced to marry through their partner’s fraud, misrepresentations or missions; or (2) When a person purports to marry or cohabits with another person ... and is also engaged in some type of abuse, violence or fraud. This office will prosecute the crime of child bigamy ... regardless of whether one of the parties is also engaged in some type of abuse, violence or fraud....

This policy is intended, under the prosecutorial discretion exercised by this Office, to prevent the future prosecution ... of bigamous marriages entered into for religious reasons.