Seizing digital media is subject to local laws, if you are not a member of law enforcement (and even if you are!) there are limitations on what you are allowed to seize and how to go about it.

Mobile phones in a UK evidence bag
Warning Whilst this book will give you a brief overview of seizure it cannot be construed as strict legal advice. Make sure you do your own legwork on local law/custom
Introduction to Digital Forensics
Seizing digital media