When David is fumbling through the jars looking for the keys to unlock the chained up motor bike, he frantically ly searches for the keys. A few seconds later, it clearly shows a combination lock falling to the ground.
Well, for one thing, many combination locks(especially the ones at school) have a master key in case you forget the combo for the lock. It happens a lot at my school and the janitors get really frustrated at us.(something about making their lives miserable?)Anyway, Sarah's dad might've forgotten the combo and had to use a key. It's very possible that that happened. SO this really isn't a slip-up.
They do make combination locks which can also be opened with a key in case the spindle is damaged and cannot rotate or the combination is forgotten. In my high school gym class, we would secure our lockers with such locks. We opened them with the combination so no other students could get in, and the instructor would open them with the keys so he didn't need to fumble with a list of several hundred combinations. Some combination locks which also use a key are the kind where the key is used to change the combination, like regular school lockers with built-in locks where the combinations are changed before the start of every school year.
HIS CHARACTER WAS LEO!!! NOT DAVID!! How in the world did you get David From Leo. If im not mistaken, there wasnt even a David in the movie. Maybe there was, but still, his name was Leo. Did you not pay that close attention? Sorry, wasnt trying to be nasty there, just trying to prove my point. :)