There are probably thousands of profiles with kill in the name. Facebook does not have minority report style pre-crime department. At the best they can do is ban or suspend the profile asking for a name change, that too only when other users report the profile. And banning that profile also wouldnt stop any crime. What you are asking for is minority report.
Zuck is watching your wife cheat on you via the Portal you setup in your bedroom. Then the geolocation tracker in your Facebook app alerts him that you’re coming home too early. He jumps into an autonomous Lyft and speeds to your house, breaks in through your bedroom window, and arrests you right as your about to stab your cheating wife to death.