One of the best place to check the statistics is the local policy department Usually Chamber of Commerce/Visitor Center is also very helpful. I would also suggest that you talk to a few neighbors around the area and find out about the neighborhood situation.
This is a recent post with a few sites for crime rate.
I also suggest that you check Megan's Law site ..
There is a link to this website and many other great search tools on my website, http://www.UphamRealEstate.com.
Hope this helps!
Here's the link to the Alexandria, Virignia Police Department web site and crime statistics - http://alexandriava.gov/police/pd_crimestatshome.html.
You can also talk with those who live in the neighborhood you're considering. Perhaps a drive out on a Saturday or Sunday afternoon to chat with those washing their cars or hanging out on their deck...