One of the nice things about the internet is that IP addresses can't be (legally) tied to the person using it.
Smartphones are personal devices, and without SIM cards a network connection can be tied to the person using it. This is a fundamental change and we should think hard if we want that to happen.
I'm sure it's not all the evidence they had. You can definitely use an IP to aid an investigation but there's too much plausible deniability for "beyond a reasonable doubt" if all you have is a computer or an IP associated with a crime.
Smartphones are personal devices, and without SIM cards a network connection can be tied to the person using it. This is a fundamental change and we should think hard if we want that to happen.