Continuity mistake: The pile of clothes that falls onto the remote control car changes between shots. The hamper turns over as well. (00:37:35)
Continuity mistake: Alex opens the closet to get his mum's coat, and the big red boxing glove springs out. He then picks up a black pole from the floor in a closeup ... which wasn't there in the previous wideshot. (00:56:30)
Continuity mistake: When Beaupre is approaching the pile of clothes that has the remote control car under, Alex rushes to the attic window and uses his remote control to turn the TV on in that house, to stall Beaupre. There is an item on top of the TV and in front of it too. These two items disappear as Beaupre approachs the TV. (00:38:00)
Continuity mistake: When Alice does flips to try and get on to the back porch of the house, her hair is different after she turns around to walk towards the door.
Continuity mistake: When Alex revs the toy car backward to drag the rug over the stairs into the other room, we can see in one shot the rug only reaches the bottom of the second step, whereas in the next shot of the car coming down the steps, the rug is now further down and you can see that a ramp has been put under it so the car does not fall over. (00:36:15)
Continuity mistake: When Alex's Dad arrives home at the end of the film, he hands Alex a remote control car box. Between a wideshot and closeup the box turns around 180° in his Dad's hands. (01:32:10)
Answer: It was Jernigan who thought there was a woman in the shower and he couldn't take the risk that if it was a woman, that she would eventually get out and see intruders in the house and call for the police. The only option open to Jernigan would be to kill her so there'd be no witnesses.
No it was Beaupre who thought there was a woman in the house.
I've seen the movie and I can confirm that it was Jernigan who opened the shower curtain because he thought a woman was in the shower.