Is releasing photos of someone and accusing them of murder really not considered libel in the US? It seems like quite an extreme case of libel to me (although IANAL).
Freedom of speech is kind of a big thing around here, yes.
You have to remember the context: Some nearly anonymous asshole points a finger and says that so-and-so is the bomber, with no real concrete evidence. It's practically a farce at that stage, only idiots could fall for that.
Unfortunately for Sunil, there are a lot of idiots online (and in the media, apparently).
On the other hand, entities like the NY Post should have known better. They presumably pay "journalists" to fact-check (so there's a higher standard of quality expected), and they understand that it imparts a higher expectation on what they do print, which means it's more likely that people would believe such an accusation.
So Sunil might even have a case against professional outfits like these, especially since he wasn't previously a public figure. But against random people from the Internet there's not really any hope of a libel charge sticking.
Maybe some states would have "cyber-bullying" legislation that would apply though (assuming it's not struck down as unconstitutional).
> Is releasing photos of someone and accusing them of murder really not considered libel in the US?
It depends on the particulars of the accusation, but probably not.
Saying "I think you killed her" is a statement of opinion. If that is an opinion the speaker legitimately holds, then it would probably not be considered libel. Generally libel needs to be both false and malicious.
Proving malice is hard, so libel/slander is usually a difficult case to win. That's one of the things that makes it different than other venues, where intent (and sometimes even falsity) are not required.