Example 1: In countries that had little formal legal structures and rudimentary identification (e.g. India in the early 1800s), it was incredibly easy to be a criminal and just move from town to town while acquiring new identities. In other words, there was a huge upside to becoming a career criminal since it was both difficult to catch you (no forensic evidence) and even if you were caught, you could just reboot your life.
Example 2: He mentions a case where a gentleman was charged TWICE for crimes that were later found to have been committed by someone else who had only a passing resemblance.
I read this book before Twitter/Facebook became ubiquitous and every like, share, comment was public knowledge but even at the time, it was mind boggling how different "identity" was back then.