One easy way would be to replace the HDD. If you can't do that, maybe just monitor the network traffic once it's online. Don't forget that many hackers also mess with electronic like the TinyDuino, which can fit inside a laptop case, it's unlikely, but it's still possible.
If you feel that the laptop or HDD isn't safe anymore, zero the drive or toss it.
What you are describing is called an Evil Maid attack.
The short answer is NO: you cannot trust them.
The long answer is MAYBE: depending on the hardware manufacturers of your devices you can verify the integrity of the data and the firmware of their components. However, I still not know any easy solution for all of them as a whole.
For the BIOS and ...