MB3 158a: When can you use Something that a Gentile did for you on Shabbos (325:5-7)

If a gentile trapped an animal on Shabbos you can't benefit from it on Shabbos because of muktzah. Benefitting from it after Shabbos. What if we don't know if the non-Jew did the melacha on Shabbos or if he specifically did it for the Jew.