You can find Pittsburgh City crime stats here: http://www.pittsburghpa.gov/police/crimestatistics.htm
Seriously though, I'm always cautious when clients ask about this. It's important to realize that it's impossible to give any sort of guarantee of safety, which is often the real motivation behind the question. All a Realtor can do is refer buyers to third party sources, and recommend talking to the neighbors (though I'm not sure how they're supposed to bring up the subject casually with strangers), as the other respondents have done.
I've posted on this before. The registry has a very broad spectrum of offenders, from "real" ones (actual pedophiles) to pranks (mooning a cop or something), to teenager minors caught having consensual sex. Not everyone on it is dangerous. And of course, they have cars and can drive anywhere. And nothing stops one from moving in the day after closing. And the registry only has ones that have been caught, etc.
You and all are encouraged to look up this list for anywhere you my live or move to. However keep in mind that strangers are a small portion of those we need to keep away from our children. In the majority of cases abuse is from friends and family. 94% is the last numbers I have read.