Factual error: Upon finding the cordless phone's base in the shed outside Mark's neighbor's house, the cop says, "There's the transmitter, which means the receiver could be in any house within 1,000 yards of here." I noticed no amplifier or anything to soup up the transmitter, and I know of no store-bought cordless phone with a range even remotely close to 1,000 yards. (01:09:05)
Factual error: When Christian Slater is talking on the phone in one scene, it is clear it is a cordless phone. When he slams it down, however, it makes that "ding" sound like older phones that really have a bell in them.
Chosen answer: Well, with no actual scene where he confesses, it's left up to us to wonder. Personally, I find it unlikely that he'd actually admit the whole thing to his parents, but they're not stupid and already had their suspicions, so the lack of any great surprise on his father's part isn't unreasonable. You also have to remember that Mark's voice changer had already broken before they drove down to the crowd - his father would have easily recognised his voice before his actual arrival, giving him a certain amount of time to get through the initial shock.
Tailkinker