Continuity mistake: The main bad guy has Alex cornered in Mrs. Hess' garage. Look at the clear plastic cup behind Alex. One shot the cup is upright, the next it is on its side.
Continuity mistake: When the villain with the long hair is being electrocuted by the wire outside the front door, in a close up shot his ski pants are on fire, then in a further away shot, they are not, then in another close up they are on fire again. (01:03:05)
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.