A WorkFlow can be set up to create a People record every time a contact is added with a Category of Witness. When a People record is created, it requires a Client ID be selected for it to proceed. Once the Client ID is selected, the record can be created and saved automatically or be left open for additional information to be added before saving the record.
To automatically create a People record based on a Witness Contact Category
You now have a WorkFlow that will automatically create a People record for you when a contact is added as a Witness.