Legal Question in Landlord & Tenant Law in Illinois

If you have a written lease I'll bet you there is some provision in it about the landlord's not being responsible for theft, especially in an area shared by all the tenants (a "common area"). Check your lease first. However, once the landlord is on notice that there may be a thief among the tenants (or from the outside) the landlord may be under an obligation to secure the garage and give access only to the tenants. But that's not clear from the situation. Have you spoken to any other tenants about their missing things? Maybe worthwhile.