Neighbor Catches Man Trying To Bury Woman Alive in Trash Bag

by Jeff
(Massachusetts, USA)

What is the movie where a guy kills a woman and tries to bury her, but a neighbor or friend comes to talk to him and the trash bag she is in starts to move so he hits it over and over trying to make it stop? She then comes back as a big purple monster.

In one scene, a boy is taken through the bathroom mirror by a zombie/monster soldier from Vietnam and the man follows him through the mirror to get him back.

Any ideas?