II think that serial killers were smarter and of a higher caliber (and certainly more patient) than the mass shooters of today.
Look them up -
Wayne Williams – Atlanta child killer – 1979–1981
Aileen Wournos (Florida, over two years)
John Wayne Gacy
Cleveland Torso Murderer (several years in the 1930s, never caught)
Ted Bundy
Son of Sam (Berkowitz)
Green River Killer (Gary Ridgway)
Zodiac Killer (never identified)
Boston Strangler (diSalvo)
Hillside Strangler (LA late 1970s)
and many more,
But what they tend to have in common is that:
(a) they planned ahead, didn’t do spur-of-the-moment killing usually
(b) they were patient – their killings were stretched out over months or years (Green River killer, over decades)
(c) usually, but not always, they buried or hid their victims
(d) almost all men – except Aileen Wournos)
(e) Usually not motivated by religion or drugs. These people were clear-eyed killers.
Mass killers today (2023) act on impulse, they don’t plan ahead, like they’re getting a drug rush from the killing. Very uncultured and unsophisticated.