Employment Law Questions? Ask an Employment Lawyer.
That would be difficult to say definitively without knowing all facts in a situation. Normally, materials created on an employer's computers or premises to help perform the job one was hired to perform is considered to be the property of the employer, not the individual employees of the employer or their supervisors. However, there may be individual contracts created or entered to by a supervisor and an employer that may make some things personal property of an employee.