Dear Neeta,
As mentioned by other users, first check the nature of the crime, i.e., civil or criminal. If it is a criminal offense, there is no need to give any explanations; however, make sure you have written evidence so that you don't get into any problems later. Regardless of the cadre or position the person holds in the company, if found guilty, the company and management have the right to expel the individual from the office.
The other aspect you have to check upon is the terms and conditions mentioned in the appointment letter. Normally, it states that both parties must give one month's notice when a decision to leave the office takes place, either voluntarily or involuntarily. So, keep this point on the checklist.
Make sure to gather necessary information from colleagues (intra and inter-department), from his official system, i.e., scan the system, so that you have substantial evidence about the activity.
Intimate everything in writing by marking a copy to his immediate supervisor and to your supervisor.
Document the same in hard copies in his individual file along with necessary signatures.
Ensure a formal email or letter goes to every department in your organization either directly or indirectly related. If possible, limit this activity to the department heads so that lower levels in the organization don't get panicked and start discussing. This might result in employee demotivation.
After you perform all the above-mentioned activities, make sure to speak to the accused manager's immediate subordinates and his team to ensure them that job insecurity arises only when an employee is associated with a crime, either civil or criminal, which affects the reputation of the company as a whole. This will show that the company, in line with the HR department, is concerned about the other employees in the department.
I hope the points mentioned will be of some help to you.
All the best.
Regards,
Suresh