Rampage/Spree shooters, mass murders, terrorists...
I think some of the misunderstandings or conflicts about these events come from how you define the labels or terms.
I'd call a subject a spree shooter if they "snap" or "wig out" then start shooting at random people they don't know.
A "mass murderer" would be someone like the Fort Hood Texas officer or the LIRR shooting event subject(who used a Ruger P85 9x19mm pistol). These are criminal acts & maybe terrorism. They used a plan & prepared to kill unarmed people.
In the mid 1990s, there were a series of USPS employees who; "went postal".
Those may be brought on by stress, PTSD or mental health problems.
Crazy people can't "go crazy" on command & they can not buy firearms, load ammunition, draw maps or make plans, drive vehicles THEN claim to be "out of it". Prosecutors & most judges don't buy that BS.
ps; LTC David Grossman's non fiction books are worth reviewing. They offer great insight to armed professionals.