If all the individual files that you were wanting to nuke the 1st and last 2k on were in the same folder, probably not very long.
The problem with said scenario is that when the police are "at your door", they're usually not simply at
the door for a very long time-period - they're through
it (don't get me started on the demise of "knock-and-announce" - http://www.cnn.com/2006/LAW/06/15/scotu ... index.html
- recently, this was the cause-of-death of a 92-year-old woman in Atlanta: http://www.11alive.com/news/news_articl ... ryid=88091
So definitely don't make a run for your computer when the door gets busted down - it'll probably be the last thing you ever do.
Also, it would require a massive amount of sangfroid to be able to accomplish the partial erasure of the files under that kind of stress - and would it really
do any good? All the rest of the information would still be on your HD, and available for recovery (albeit they'd have to work a lot harder for it).
Given the fact that you're probably going to be sound asleep when the door comes off the hinges, I really think this is all pretty much a moot point.
The only way to not have to worry about stuff like this is to not
have anything on your computer that'd ever draw that kind of attention from the authorities - period. (Or to have such material totally encrypted, which is a total PITA). Pete