Slow motion Pabst

I just watched the 140 minutes version of this great film. It is the first time I watch a movie by Pabst, but, since always, I have heared the best things about him. I was wondering if he was the first one to use Slow motion so often in his scenes, or was there some other director making it before him.
This one is just one technique amongst lots of others used in the movie.
PD: which movie should I watch next out of Pabst's filmography? I was thinking in Pandora's Box.