Thank you all for the fast replies!
In each Trulia house listing, there is a map that has multiple tabs showing local schools, comps, crimes, etc. The Crime maps are color-coded from green (no crime) to red (high crime). They also show individual crime locations. But many of the red areas don't show any individual crimes. There was a box for questions below the Crime map, so I asked. I meant the question more for Trulia than individual replies, but since the question appeared here, maybe someone can answer it for me.