Many of these knives also store backup blades in the handle. Other designs, such as foldable box cutters, use a locking clip ...

(CNN) --The complex investigation into the terrorist attacks in New York and Washington gathered more strands of evidence over the weekend, leading authorities to several parts of the world.

They found an open box cutter knife with blood on the blade, a broken knife handle and a screwdriver. “You can tell there was a lot of rage just based off the scene,” said Carrillo.