Facts.
It was all about the thirteen facts.

Fact number one: He had an alarm system. It ran throughout his house, and was very easy to set off. If a single window, or door was opened while the alarm was active, it would blare loudly.

Fact number two: He was all alone. At three in the afternoon, his mother left for work, and he was left home alone. He was an only child, and his parents were divorced when he was younger. His mother got back home at ten at night. She always set the alarm before she left.
These two facts alone left him both vulnerable, and protected at the same time. He never feared an attack from an intruder.

Fact number three: He was only thirteen. This left him even more vulnerable than he thought. He was confident, like anyone else would be, that he was safe. The truth was, he was never safe. Since the day he was born, the course of his life was set.