Summons for receiving stolen property without knowing it was stolen?

I was at work when my girlfriend had a friend over who was having problems at home. She brought some clothes and other items including a broken safe. When i got home she asked me if there was a trash dumpster outside where she could throw away the things she didnt need. I told her not to throw the metal safe in the dumpster but beside it with the other metal appliances. A few days later cops and my po are searching my house for stolen property.To make a long story short the safe was stolen from her mother. i had no idea of this and the girl owned up to stealing the safe and placing it behind my house and told the police i had nothing to do with it and did not know that it was stolen. now i have a summons for receiving stolen property and that is a violation of my probation.The summons is petty however the violation will result in me going to jail for four years unless the charge gets dropped. im not sure what to do i already told them i had nothing to do with it and didnt know it was stolen and so did she. The particular cop has had it out for me for some time and i dont want to be convicted of something i honestly had no idea about. What should i do?