Police around the world investigates big data digital evidence using NUIX. Proof Finder is a basic NUIX software tool released as a philanthropic project for 100 USD per year, which allows to learn main functions of NUIX with databases up to 15 GB. Proof Finder can handle data from mobile devices, hard drives, forensic images, file shares, Microsoft Outlook, or Lotus Notes, and complex storage systems, e.g. importing data from XRY or UFED. Proof Finder provides capabilities required for forensic analysis of disk images, including recovering deleted files, carving unallocated space and unidentified data items, fully indexing and navigating Windows Registry files, and a hex viewer to analyse files and file fragments.