Your statement is just plain not true.
The media would like us to believe that it is true, and that is the agenda they push, but the Zodiac serial killer was black, the DC snipers were black, etc.
The latest Denver school shooters were "gender confused" but that was quickly covered up and the story has died. Can't be having a favored victim class be guilty of anything.
Don’t forget Wayne Williams, who is thought to be responsible for more than 20 murders (he was convicted for two); he’s black, as were his victims. The Railway Killer was a Hispanic man who killed probably upwards of 16 people; he was executed here in Texas.
There is an article from Psychology Today from 2014 that describes the idea that serial killers are almost all white males as a myth.
The author ascribes this perception to white killers becoming “cultural icons” (such as Ted Bundy) and to biased media.
I don’t know how to post a link, but it’s an interesting article.