I haven't used it in some years now but I suspect it's still the same. Snapchat is a messaging platform with the main form of communication being images showing what the user is doing at the moment, either through direct message which disappears after the receiver views the picture, or through a "story" which is removed after 24 hours. You can send people direct/private messages with just text (and stickers, etc.) as well and those conversations disappear after both parties view the messages and leave the chat page. You have the option to set your stories as "private" so only friends can see it, and you assume a "private" message between you and another user is "private", or the image you sent to your friend will only be seen by your friend. But people forget (because nobody reads them) that it doesn't mean they didn't agree to T&C that tell them that nothing they do on the platform is private and they give snap inc the legal right to use or sell their data. They don't advertise E2EE, but I'd say a majority of Snapchat users either don't care to understand the value in E2EE or they have never heard of it and don't even know what it is.

If I overheard some kids making obvious jokes about shooting a kid at their school while sitting in a public area, I would do nothing, "kids are dumb, they shouldn't say that shit because it's a sensitive subject, but obviously they're not being serious" I would think.

If I overheard them planning a murder of a fellow student, or of anyone, whether with a gun or any method, I would be inclined to call authorities and report it.

Imo, this situation is wrong, it shouldn't have happened, no planning occurred, it was just a joke, as tasteless as it may have been, it was still just a joke to let off some steam. A crime would have been if they made an elaborate plan on how they'd do it, like waiting for the kid to be alone, and talking about ways to do it without getting caught or saying they would bring a gun to school tomorrow and shoot the kid, these sentences all have planning involved. Saying I want to kill myself after an embarrassing moment or kill someone else after they hurt my feelings doesn't justify someone calling the cops on me because they fear for my or someone else's safety and now they've ruined my career over a thought that slipped out of my mouth during a moment of emotional distress.

People should be seeing this story and boycotting Snapchat, users stories should be riddled with links to this story and educating friends about why online privacy is important and how to protect themselves, but it won't be, I'm sure most will not ever even hear about this story. Plus, the comment this person made is obviously controversial so there's a lot of differing opinions about whether it was okay to say that to someone in a school setting, but this isn't about that at all, it's about privacy, doesn't matter what was said, doesn't matter where it was said. What matters is that a person said something to another person in confidence and without either of them realizing someone else was spying on them, like a bug being planted in someone's home. The conversation didn't happen at a school, it happened on the Internet, in a "private" room.

Preventing crime is and should be a tricky business, because if it was easy then that would mean nobody would have any privacy, physical and digital locks would have to be purchased from the government so they could access anything you have. Houses and cars would be required to have microphones and cameras that our governments would have full access to. Nothing we said, did, or owned would be private. Nothing you invented would be yours, nothing you build would be yours, and nothing that makes you happy/sad/angry/embarrassed/etc. would be yours.

This is blatant proof you are the product and everything you do on the platform is surveiled. Individuals are not as valuable as communities, so ridding their platform of one person means absolutely nothing to them even if it ruins the individuals life in the process. If they started the platform with these controversies, they would have never gotten traction. They got traction because the mechanics of the system give you the impression that you are talking privately and everything you do on this platform "disappears" into nothingness and you don't have to worry about an embarrassing picture or message coming out years down the road.

Sorry for the long winded response lol

TL;DR Snapchat gives the false impression of private conversations that disappear forever, sort of like how signal can be configured, but it has a higher priority for image sharing, and of course, nothing is encrypted so nothing is really ever deleted. It doesn't matter the individual was at a school when they said the thing, the context of what they said is important, and more importantly the fact they said it in confidence is important.