What obligation does an employer have when an employee’s personal property is stolen from the staffroom by an outsider?
There is no obligation on the employer in this situation. In some circumstances, the employer’s insurance may cover it but that is not common. The employee’s personal insurance would be more likely to cover it, if they have personal contents insurance.
While theft from a workplace is illegal and could be considered a police matter, other areas of misconduct are not so black and white.