I doubt that would have helped, short of encrypting the HDD I doubt you would have stopped the guy putting stuff on it, besides it sounds like he removed the HDD to tamper with and didn't plant the evidence in situ before posting it.
I'm still confused how the guy didn't notice his HDD missing long enough for it to go throught the post and be investigated by the plod.
It raises an interesting point though, clearly the HDD has been removed from the owners premisis without his knowledge or consent, how the heck could ANYTHING stemming from that stand up in court?
The HDD was ripe to be tampered with (obvious here)...
Time stamps would mean nothing, the content would mean nothing...it's crazy!
So If I decide to rob a house but the owner wakes up and gives me trouble I can get revenge if I get away by tampering with the HDD on the laptop I stole and mailing it to the police?
(This has happened before, stolen latop with kiddie pron on posted to the plod, owner arrested and charged albeit admitted to possesion apparently but nothign to stop someone faking it)