Under Arizona law, theft/control of property generally refers to this:
A person commits theft if, without lawful authority, the person knowingly:
1. Controls property of another with the intent to deprive the other person of such property; or
2. Converts for an unauthorized term or use services or property of another entrusted to the defendant or placed in the defendant's possession for a limited, authorized term or use; or
3. Obtains services or property of another by means of any material misrepresentation with intent to deprive the other person of such property or services; or
4. Comes into control of lost, mislaid or misdelivered property of another under circumstances providing means of inquiry as to the true owner and appropriates such property to the person's own or another's use without reasonable efforts to notify the true owner; or
5. Controls property of another knowing or having reason to know that the property was stolen; or
6. Obtains services known to the defendant to be available only for compensation without paying or an agreement to pay the compensation or diverts another's services to the person's own or another's benefit without authority to do so.
Probation expiration can mean different things, depending on the status of the case. If the probation term has expired, and your nephew successfully completed all of the terms and condition of probation, then your nephew's probation should have been "successfully terminated." I recommend calling the Court Clerk's office and asking what the "expiration" means.