You have given good information however, you could have quoted what exactly was the issue? What kind of facts have been suppressed and who discovered it and how it was discovered. How will it impact your ongoing operations or image of the company?
If there is collusion between newly appointed employee and a regular employee then you may order domestic enquiry. Let the facts be investigated independently and impartially. Based on the outcome of the enquiry, you may take suitable disciplinary action against trainee as well as regular employee.
Once again I appreciate about clarity of your post. Such posts and few and far between at least on this forum.
1st March 2018 From India, Bangalore
Enquiry can bring out facts and based on report action can be initiated.
1st March 2018 From India, Pune
1st March 2018 From India, Hyderabad
2nd March 2018 From India