Stitch has episodes throughout the movie causing him to destroy stuff.
On a couple of occasions, Stitch slashes his claws across Lilo's face, leaving scratches in her cheek.
On the DVD is a short, "The Origins of Stitch", and Dr. Jumba explains that the genetic material came from a variety of horrendous monsters. The creature that provided the arms, hands, and claws looks frightening, and Stitch stares at his hands and claws and sees that they are exactly the same as the monster's.