E2E is only as trustworthy as the endpoints:

Undercover NYPD infiltrated small groups of Black Lives Matter activists and gained access to their text messages, according to newly released documents obtained by the Guardian. ...

...Undercover officers were able to pose as protesters even within small groups, giving them extensive access to details about protesters’ whereabouts and plans.

https://www.theguardian.com/us-news/2017/apr/04/nypd-police-black-lives-matter-surveillance-undercover

@sarahjeong I'd be surprised if they were using end to end encryption, but I get you're point. Clearly it takes a lot more than just e2e encryption to plan this sort of stuff securely.

It seems to me most likely that one of the organisers was an informant (rather than any police actually posed undercover).