What can I do legally about losing my job due to an employer's zeal?

Unfortunately there is probably not much you can do. Any action you could take would have to be in a civil court, not a criminal court, where the burden of proof is a lot lighter. If it were criminal court, they would have to prove beyond a reasonable doubt that you had stolen the merchandise, plus the way they word it isn't even that you actually stole it, you just had it somewhere that it should not have been. In civil court, they would only have to prove that it was "likely" that it was your doing, not definitely you. So even though the BOL did not rule against you does not mean that a civil court would. You can definitely still speak with an attorney but with the burden of proof being so light, chances are any claim for damage you made would be dismissed.