Staircase Dismemberment

I remember flipping through the movie channels when I was younger and caught a portion of a horror movie where an attacker was under the stairs hacking at a victims torso while their friends tried pulling them up from the stairs they fell through. It seemed like the attacker was wearing a skimask or something similar. It seems very possible it could be Torso. Does anything like that happen in this movie? If not, does anyone have a clue what movie I'm looking for?