linux - I can't find the ghosts taking up space on my hard drive

No Free disk space

$df -h

returns

/dev/sda1              16G   16G     0 100% /
tmpfs                 502M     0  502M   0% /lib/init/rw
udev                  497M  116K  497M   1% /dev

tmpfs                 502M     0  502M   0% /dev/shm
/dev/sdb1             2.0T  886G  1.1T  47% /srv/ftp
/dev/sdc1              16G   12G  3.9G  75% /var/opt/CrushFTP6_PC/TempAccounts

then

$du -hs * | sort -rh

returns

886G    srv
12G     var
838M    usr
119M    lib
15M     boot
5.8M    bin
5.6M    etc
4.6M    sbin

2.4M    lib32
120K    root
116K    dev

The 886GB is on /dev/sdb1

the 12GB is on /dev/sdc1

Please help me figure out where the space is going on /dev/sda1. Are there files that I deleted that are still in use? If so how can I find them?