OS X | Impossible to empty my trash

Question

There are four folders in my trash which are resisting any kind of deletion. So far I´ve tried multiple ways but im still stuck. I already searched for the same problem on superuser but so far no solution worked out for me.

At first I tried to delete the files within the directorys and then the folders themselves. The ~/.Trash/ file I want to empty/delete is the one on the external hard drive, the startup volume is fine.

rm -rf ~/.Trash/*

Doesn´t solve the problem.

At first I tried to delete all normal and hidden files within the directory with:

sudo rm -Rf directory/*
sudo rm -Rf directory ./*

Then delete the directory/folder itself with the same command above results in "Directory not empty". How can that happen when deleting all files recursively ?

I checked if there is any files left with ls -la but except "dot files" there is nothing left. Read-Write-Execute is enabled on any folder for everyone.

There is no process accessing any file on my external volume...

lsof | grep "/Volumes/MyVolume"

I can´t tell how the files happend to be at this undeletable state. The last solution I know is to format the harddrive but I wan´t to avoid that because there must be a smarter way.