No animal may be declared dangerous if the threat, injury or damage was sustained by a person who at the time was committing a willful trespass or other tort upon the premises occupied by the owner or keeper of the animal, or if such person was teasing, tormenting, abusing or has in the past been observed or reported to have teased, tormented, abused or assaulted the animal or was committing or attempting to commit a crime. Neither shall an animal be declared dangerous if, while under control of a qualified trainer, in use for public law enforcement, it inflicts damage upon a person who is committing a crime.