The First Officer (FO) stated that they had completed a short 5 minute flight in the local area and performed an uneventful instrument landing system (ILS) approach to runway 16 at the Asheville Regional Airport (AVL) Asheville, North Carolina. The FO stated that they performed a normal taxi-in until they arrived out in front of the "Bulk Hangar" facing south where they shut-down the airplane using the normal shut-down checklist. The FO said that he spoke to his son, the Pilot-In-Command (PIC) of his intention to get up, open the cabin entry door, and secure the airplane with chocks once outside. The FO got up out of the right cockpit seat and started towards the main entry door in preparation to open the door. He stated that the PIC "also started to leave the cockpit when [the FO] realized that the airplane was rolling and alerted [the PIC] that the airplane was moving." The PIC "got back in the left seat in an attempt to stop the aircraft." The FO stated that the hydraulic pressure was in a "diminished state" and the PIC could not stop the airplane in time to avoid contact with the fence. When asked if he knew why the airplane started to move, he stated that he "believes that his son, [the PIC had] assumed that [he] had opened the entry door and completed chocking the aircraft wheels." According to the FO, the PIC "mistakenly released the parking brake which had been set during the normal shutdown checklist procedure." The PIC refused to provide a statement to either the National Transportation Safety Board (NTSB) or the Federal Aviation Administration (FAA). Both the PIC and FO were requested to provide an NTSB Form 6120.1 Pilot/Operator Aircraft Accident/Incident Report in accordance with Title 49 Code of Federal Regulations CFR Part 830.5(a). The report is required to be filed within ten (10) days after an accident for which notification is required by Section 830.5 or when, after seven (7) days, an overdue aircraft is still missing. But at the time of this report, the reports had not been received by NTSB.