Forensic investigations are always challenging as you may gather all the information you could for the evidence and mitigation plan. Here are some of the computer forensic investigator tools you would need. Most of them are free!
SIFT (SANS investigative forensic toolkit) workstation is freely available as Ubuntu 14.04. SIFT is a suite of forensic tools you need and one of the most popular open source incident response platform.
Volatility is the memory forensics framework. It used for incident response and malware analysis. With this tool, you can extract information from running processes, network sockets, network connection, DLLs and registry hives. It also has support for extracting information from Windows crash dump files and hibernation files. This tool is available for free under GPL license. 1e1e36bf2d