When Cayetana and Phillipe come back to the house after school Cayetana looks at his computer. His laptop has, presumably, been sitting open, all day, unplugged, without the battery dying and with no password. Most laptops will not stay powered on that long (they'll shut themselves off to conserve power). Also, for someone willing to film a stranger because of security concerns he certainly would have some type of password feature to unlock the system.