[masukomi]

They have physical access to the device. They can enter recovery mode by holding down command r when restarting. It gives them a different copy of the os with multiple apps that you can type in (like the terminal) and would allow superuser access to whatever they wanted, however your encrypted home directory would remain encrypted and they would not be able to read it. In the olden days you would stick in a recovery cd and reboot onto that... you could also (historically and presently) stick a USB drive into the thing and boot into an os on that.... NEVER give out your password.