They did it in the dark. Our neighbour has now installed a light in the back to try and prevent this from happening again. After it happened we also installed one of these automatic lights that goes on as soon as it senses someone moving nearby. The police suggested that. They like working in the dark.
Darkness is the criminal's friend.
If you're going downtown at night, don't walk in a dark area alone. If you're out jogging or biking, stay to well lit streets or bike paths. It's safer that way. Darkness - where you can't be seen. That's where criminals like to do their work of stealing and hurting and breaking.