Here's a deleted scene
from Let Me In
via /Film that includes additional commentary from director Matt Reeves explaining why he had to cut it.
Interesting, the scene contains two blink-and-you'll-miss-it shots from the trailer that weren't in the movie: An evil face looking straight at the camera's POV and a close-up of Chloe Moretz screaming while pinned to the floor. It's quite haunting and beautiful shot, like the rest of the movie.
... for a little while."