The "black-clad, pale-skinned, basically depressed-looking, given to eyeliner" definitely describes the goth stereotype. For example, take this character from the British TV show The IT Crowd, where most characters are caricatures of stereotypes:
Checks all the boxes (though maybe not depressed-looking in this picture).
Thanks to the links from Rand al'Thor, we can also explore the connection between (or lack thereof) the Columbine shootings and the goth subculture. Soon after the massacre, there were a number of misconceptions floating around about the motivations of the shooters, such as subversion by the goth subculture, reaction to bullying, and so on. The Wikipedia article mentions this:
Debates were sparked over gun control laws and gun culture, high school cliques, subcultures, and bullying. Also discussed were the moral panic over goths, social outcasts, the use of pharmaceutical antidepressants by teenagers, teenage Internet use and violence in video games and movies.
The apparent goth connection came largely from a group in the school named the Trenchcoat Mafia. From an April 1999 article in The Guardian (be cautious of the article, it's from right around the time when these misconceptions were strong and I'm using it show how things were then):
And, right at the bottom of the food chain, there were the students
who could not fit into any of the other groups, the quiet, brooding,
According to pupils who spoke to the Guardian last night, these pupils
were invariably shunned by the other tribes, and frequently bullied,
verbally and physically. As a reaction, they formed a clique two years
ago and called themselves the Anachronists. But it was the derogatory
label given to them by the jocks because of their habit of wearing
long black trench coats whatever the weather, indoors and out, which
stuck: the Trenchcoat Mafia.
... Central to the Trenchcoat Mafia's identity was their association with 'dark metal' Goth music.
The Washington Post article suggested by Rand al'Thor shows what they reported then and corrects it:
The Washington Post put it this way: “The shooters who turned
Columbine High School into an unspeakable landscape of carnage
yesterday were members of a small clique of outcasts who always wore
black trench coats and spent their entire adolescence deep inside the
morose subculture of Gothic fantasy, their fellow students said.”
Harris and Klebold knew a few of these students, but they were not
considered core to the friend group, the Jefferson County Sheriff’s
Office later determined, and did not appear in a photo of Trench Coat
Mafia members in the 1998 yearbook. Most of those students had
graduated the year before the shooting.
Police also later determined that some students confused Klebold with
another student who was in the group and resembled Klebold.
This Salon article goes into a lot of detail about this and some other misconceptions.
Investigators also criticized the media for propagating the myth that
the pair were Goths. Apparently it took nothing more than reports of
black clothing and eyeliner among the unrelated Trench Coat Mafia for
much of the national media to label them Goths. "That became a whole
issue for a week," one investigator said. "Marilyn Manson canceled his
ABC's "20/20" aired a particularly ignorant "report" the night after
the tragedy, linking the killers to the scene with alarmist messages
about Satanism and cults. Aside from the fact that the report
completely misrepresented and maligned the movement, neither Marilyn
Manson nor the Goths had anything whatsoever to do with the killers,
who had nothing but contempt for the music.
I am at a loss as to what "sniper material" means.