e36 has 3 master locks I.e. Driver's door, front passenger door and the boot. Unlock anyone will release all locks. So any of the front passenger unlock the door, the boot is unlock too, just tekan the boot butang and the boot will open. Incar boot release is really not necessary.
My e90 is a different setup with no master lock at all. Unlock all doors require a press of button on the dash, same as lock all doors while stationary. Boot will unlock when this button is pressed. It may be deem dangerous to unlock all doors just to access the boot, hence the creation of the boot unlock button at the footwell.