I knew the key and would readily input the key frequently in the past so that I could access my information, but now that you want that information I have conveniently forgotten the key.
Yes, they would put you in jail, but more for being a bad liar than for having a faulty memory.
What if you used it before, but not like yesterday? What if you last used it a month ago? A week ago? What is "frequently", once a day? Once every two days? Once a week?
