The City of Oakland publishes crime watch data on the City’s web site. You should start by reading the disclaimer and go from there. You can check by type of crime, by date range, and specific neighborhoods.
For some background on the application, see this SFGate Article.
Jenn Shreve’s Salon article poses the critical question, “What good is a site that lets Oakland, Calif., residents check on neighborhood crime stats if the people in those neighborhoods aren’t online?” Shreve goes on to interview Barry Kriberg, president of the National Council on Crime Prevention: “Rather than help neighborhood groups attack crime problems, Kriberg says the site will probably prove most useful to people deciding where (and where not) to buy homes or to insurers looking for an excuse to raise rates.”
Well, my own take on this is that I never met an insurer who needed an excuse to raise rates. As for folks being able to do research before buying a home, I see that as pretty much a good thing. One of the issues I’ve found in the other market I write about, Sacramento, is that often we get many folks from out of town finding the most inexpensive houses in inventory, and sure enough, those homes are located in the most crime-ridden neighborhoods. Of course, that’s a mistake that any beginner to the area can make, but the more people get interested in a neighborhood, the more issues like quiet and safety become important to find out about.