There's an old movie where a teacher and her class are pursued by killers in animal masks. Know the title?

The masked men murdered an old couple, I remember. They killed one of their own too that same night (his body detached from his head and the kids saw it). At the end, the class makes a last stand in a cave and kills the last man. They mutilate him and even keep some of his organs in their classroom science jars.There's an old movie where a teacher and her class are pursued by killers in animal masks. Know the title?
The movie ';Fortress'; with Rachel Ward as the Australian school teacher, I haven't seen this movie in ages! Makes me wanna see it again!There's an old movie where a teacher and her class are pursued by killers in animal masks. Know the title?
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