They *may* have a case against you: it depends in large part on credible evidence about your knowledge and intent. Theft is still theft, even if the theif returns the goods promptly; but it is only theft if you know, or had reason to know, you could not take those goods. If you reasonably throught you could take them (e.g. they were being discarded; they were a "tip" to you; custom is the musician can take left over bottles; etc.), then that would not be theft, since theft requires a criminal state of mind.