If this happened to me and I feared an investigation, I'd rip the hard drive from my computer and get it out of my house, immediately.

DO NOT try to wipe the drive. After a recent investigation done on MY computers (even one that had been reformatted and software reinstalled 6 months earlier) and the FBIs data recovery "expert" found every deleted file. PERIOD.

Get rid of the drive if you fear investigation. And I'm not trying to be inflammatory, just practical.