Most conventional digital forensic methods are designed to target hard disk drives, making them ineffective at detecting in-memory malware. In addition, in order to prevent a target system from changing the evidence on hard disk drives, it is necessary to shut down the system or stop its processing, reducing system availability. In this paper, we propose a live forensic method using process duplication to maintain high system availability. The proposed method duplicates the virtual address space of a target process for investigation, and obtains the relevant evidence from the duplicate. By reducing the occurrence of memory copy in the duplication process, it is possible to detect in-memory malware while retaining system availability. We describe the effectiveness of the proposed method, and furthermore, evaluate and report on the delay time when this method is applied to a periodically executing process.