The police have closed the case, and Lenny has no capacity to form a list of suspects. He keeps a huge file of information, but can't remember what he's just read. So he snaps Polaroids, scribbling information at the bottom of each. That's part of the delicious fun Memento offers. We not only discover the clues as Lenny does, but we get to determine their significance both before and after him.
Memento is a genre picture, squarely hardboiled, but with a twist.
It follows the rules of the genre, but twists them, folding back into itself, like a Mobius strip. Christopher Nolan directs from his own script, which manages to be playful while heaping surprise upon shock. Memento is not a comedy, but Nolan knows more about human nature than those forty-somethings. He knows it's possible to laugh at a senile aunt, but to still love her with all your heart. My wife, dying.