going to six different locations to shoot six different people (am I reading that right?) doesn't equal a "mass shooting" as I understand the definition of that term as a social phenomenon. A "mass shooting" is like what happened in Tucson earlier this year, or Luby's in Killeen in 1991, or Virginia Tech 2007 - it involves multiple victims chosen at random all located in more or less the same location - the classic "he just started shooting everyone".Details of the incident were sketchy, but police said the shootings unfolded over several hours at six different locations in and around the city
This multiple killing in Yuma seems more like a serial killer on a condensced time line, or a contract killer, or revenge/anger killings or something. Obviously will have to find more details to know for sure.
And the semantics of what type of shooting this was obviously don't matter to the victims and their families. But for purposes of discussing such things as social phenomenon and especially the broader context of gun rights vs. gun control, I don't think this qualifies on same level as a "mass shooting" like Tucson, Killeen, Virginia Tech etc.