Assuming that you are using us.iso.kbd keymap, you can remap CAPSLOCK to CTRL by this simple following steps.
First, copy the us.iso.kbd
# cd /usr/share/syscons/keymaps/
# cp us.iso.kbd us.iso-swap.kbd
Next, modify the permission of us.iso-swap.kbd to be writable.
# chmod 644 us.iso-swap.kbd
Then, modify us.iso-swap.kbd. Look at the line with number 058 and change “clock” to “lctrl” like this.
...
058 lctrl lctrl lctrl lctrl lctrl lctrl lctrl lctrl O
...
After that, change the permission back to read-only
# chmod 444 us.iso-swap.kbd
Finally, add this text to /etc/rc.conf
keymap="us.iso-swap"
Reboot and now your CAPLOCKS will be CTRL.