A factually similar dispute involving child pornography ended with a Vermont federal judge ordering the defendant to decrypt the hard drive of his laptop.
While that case never reached the Supreme Court, it differed from the Fricosu matter because U.S. border agents already knew there was child p0rn on the computer because they saw it while the computer was running during a 2006 routine stop along the Canadian border.
I think the Vermont case was wrongly decided, too. I don't care what the cops
saw you looking at on your computer, the point is that they're trying to get access to your hard drives in order to
see what else is on there.
EDITED to provide clarity.