What action can be taken against ex employee using data of company

One day, my manager & 15 other worker suddenly resigned & set up a competing business. They already registered a new company, found investor & purchased required machine. They used to regularly signin & then go to their newly bought office to set up things. All this while still being our employees. They were permanent employees, but no contract signed with them. They had been planning this from last 6 months, we recovered search history on our computers, showed searches for -Information for setting up company, registration process, cost of machines etc We believe our internal documents such as balance sheets & finance information was emailed out to their personal emails, as we found our Gmail "Trash" had been cleared. They have attempted to solicit our clients. They have been spreading rumours in the market. We found mistakes in our record books relating to stock & other components for the past few months which seems done on purpose. Should we try legal action, do we have a strong case?