A disavowal is a strong denial of any knowledge about something. You might use it to get across the point that you have no idea how that window got broken.
Disavowal contains the word avow, which you can use to mean "declare openly"; it's kind of the positive version of the negative disavowal. While an avowal essentially says, "yes indeed!" a disavowal is not only saying, "no," but is also implying, "I have no idea what you're talking about."