Reason for system reboot?

["Jan Johansson" <jan.johansson@nwl.se>]

Is there someway to find out what caused a system reboot? I have the
following in my "last"

argus:~# last -20
root     pts/0        192.168.221.207  Mon Mar 10 08:11   still logged
in   
reboot   system boot  2.4.18-bf2.4     Sun Mar  9 17:49          (16:06)

root     pts/0        192.168.221.207  Fri Mar  7 16:31 - crash
(2+01:18)   

But i cant find anything in the logs which shows why the system was
rebooted. What worries me more is that I should be the only one with
root access to this system, which Is a minimalistic Debian/Testing doing
not much else then running shorewall.