Just an FYI (if this post is on the level... and who knows but I digress):
As a guest in a home (whether or not it was your mother's makes absolutely no difference) you had a reasonable expectation of privacy from a search of your belongings. Even more so due to the fact that whatever was found was in a locked case. It doesn't matter that your mom found it, a stranger found it or the cops came and searched it themselves, a good lawyer will get all evidence pursuant to a violation of your 4th Amendment rights thrown out. You'll have to pay for it but you will be completely exonerated, this assumes you didn't make any self-incriminating statements to the cops when they showed up.
Here's some case info on the 4th Amendment:
In Minnesota v. Olson, 495 U.S. 91, 98-100 (1990), the United States Supreme Court made clear that a guest who stays even one night in a friend's home -- with or without a key, and with or without paying rent - "has a legitimate expectation of privacy in his host's home. That the guest has a host who has ultimate control of the house is not inconsistent with the guest having a legitimate expectation of privacy" in the home. In short, regardless of whether an adult or juvenile resided in a palatial mansion or a single room in a transitional shelter, regardless of whether he owned the residence or was allowed to remain without paying rent, and regardless of whether his landlord, friend or relative had a master key and could enter to ensure that he was abiding by the rules of the house, the guest has a reasonable expectation of privacy in his home.