Kill an stopped process

[O. Hartmann]

Sometimes it happens on my FreeBSD 6.1-STABLE/AMD box, that a process, 
in most cases xine, firefox oder thunderbird, show status 'STOP' in top 
and are unkillable!
Trying to kill them as root (sending signal 9 throught 'kill' or 
'killall') doesn't have any effect.

Can anyone help and tell how to kill such a job? The only way  getting 
rid of those processes is reboot the box and this can not be the right way.

Thanks,
oh