On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.
Off-Topic: Most stories about politics, or crime, or sports, unless they're evidence of some interesting new phenomenon. Videos of pratfalls or disasters, or cute animal pictures. If they'd cover it on TV news, it's probably off-topic.
This assassination falls squarely within politics and crime, and it's definitely something that'd get covered on TV news (and is). Clearly, some people felt that for these reasons, it's off-topic, and likely because it would be exceedingly difficult for such a story's HN comments comments to not pivot back to politics, geopolitical speculation, and the like. While stories like this have trended on occasion, there's not much substance here. While the event may or may not turn out to be relevant for all of us on a world sphere, it's more likely than not to be off-topic for this particular forum.
And yet three people posted a link to the guidelines, probably in response to "If this isn't considered suitable for HN, then a little guidance to that effect would be welcome."
Off-Topic: Most stories about politics, or crime, or sports, unless they're evidence of some interesting new phenomenon. [...] If they'd cover it on TV news, it's probably off-topic.
https://news.ycombinator.com/newsguidelines.html
Also, if you want an answer from the mods please e-mail them:
Please don't post on HN to ask or tell us something (e.g. to ask us questions about Y Combinator, or to ask or complain about moderation). If you want to say something to us, please send it to hn@ycombinator.com.
EDIT: and here is @dang calling this explicitly OT: https://news.ycombinator.com/item?id=13213437
I'll be in the HNchat.