My best friend was mugged for his phone a couple of years ago. We knew the guy who had stole it and even reported him to the police. They called the number and even asked the guy if that was his phone or if he'd stolen it.
Because he said yeah that was his phone, and that my friend couldn't outright prove it was actually his phone, the police then declined to take further action. We ended up having to corner the guy in an alleyway, threatened him with a tyre iron and got the phone back but not the sim card.
The police serve a purpose, I'm sure we're all aware of that - but they can be such a useless bunch of ****-bags when you need them the most.