The miner killer is Tom Hanniger.
At the end there's Tom, Axel Palmer and Sarah Palmer in the mine. Sarah has a gun and doesn't know whether the killer (and hence who to shoot) is Axel (her husband) or Tom (her boyfriend from ten years ago.) Both Axel and Tom yell at her that the other is the real killer. Axel goes all King Solomon and tells Sarah to shoot both of them. This confuses Sarah. Tom tries to come up with some final convincing evidence and yells out that what was written on the Valentine's Day card (which Sarah just discovered) from Megan (young girl who worked with Sarah, was having an affair with her husband and was pregnant with his child) at Axel's dad's old cabin (where Axel and Megan conducted their affair) was the SAME thing written in blood above Megan's body after she had been killed ("BE MINE 4 EVER") implying that Axel’s the killer. However, Tom made the crucial "revealing information that he wouldn't have known" mistake (see "Primal Fear", etc.) Tom wouldn’t have known that Megan was killed or what was written above her body.
Thus, Sarah knows Tom is the killer. (We then we see various flashbacks of Tom being crazy, digging up Harry Warden's body, taking his mask, committing many of the murders and locking himself in a mine cage during a miner killer attack which had previous exonerated him) Sarah shoots Tom, the bullet goes through him and explodes one of the tanks destroying much of the area of the mine they are in.
Rescue miners come into the mind and the rescue miner that first approaches Tom gets killed by the pickaxe. Axel and Sarah are seen out in an ambulance and Axel tells Sarah that Tom's dead. Finally, we see a rescue miner walking ahead of the others out of the mine with a limp (Tom hurt his leg in an earlier car crash.) When he gets to the top of the hill, he takes off his mining mask and smirks at the camera.
It's Tom Hanniger. Sequel.....?
If you're going to see this movie, pay the extra few bucks and see it in 3-D if you can.