As per the article, they definitely did call the police beforehand. Clearly the police had taken little, if any, action. It's hidden, but it's there: "my sister had already had a couple of police visits about the previous incidents".
> The confession was online
The confession was made possible via their "antics", because he knew he'd been caught. Without the experience of being cornered and having to escape, he'd have likely ignored the message as a fishing expedition.
> they already had the vehicle ID
Getting that was part of their "antics", yes.