It's often said that a dog is a man's best friend, although you can't really carry on a conversation with them, ask to borrow money, or share a six pack with a dog. However, dogs are extremely useful when it comes to crime prevention.
It's all in the nose. A dog's nose, that is. Compared to dogs, our sense of smell is pretty pitiful. Thanks to its abundance of smell receptors, a dog's snout is like a cutting edge smelling machine. For example, the typical dog is able to sniff out the equivalent of a single drop of blood in five quarts of water.
Sniffing out drugs and explosives is no big deal. Dogs that love to fetch and retrieve are best suited to this line of work. In fact, drug and anti-terrorism agents train dogs by playing tug of war with a favorite toy, say a towel that's been washed so that it has no native scent. When the trainer rolls a particular drug or explosive material inside the towel, the dog learns to associate the smell of gunpowder, cocaine, or any other illegal substance with the toy. When the trainer hides or buries the scented towel, the dog will use its powerful nose to root out the goods.
Dogs could care less about law enforcement, of course. What does rock their world is playing with that white towel or some other favorite toy. As soon as a dog on the job successfully sniffs out drugs, a bomb, or anything else that needs finding, it's rewarded with a game of fetch or tug of war. It's all in a day's work for crime fighting canines.