So while I can imagine the confusion between mosque and synagogue as being due to an honest mistake, it's hard to envision the omission of the core part of the story in the second headline to be a similarly honest mistake.
Given that "Police shot, killed 2 Palestinians" is a ****ing stupid headline on its own (Which police? Which country? What were they doing to get shot?) it seems pretty likely that the headline is part of a loop that goes something like
4 Dead in Attack on Jerusalem Synagogue.
Policeman injured in gunfight.
Police shot, killed 2 Palestinians.
If you watch the story for more than a minute it's quite clear what's going on. But if you take the picture out of context it can easily be turned into some sinister conspiracy theory.
Even if it's not part of a loop, then I'd ascribe it to the CNN headline writer being a ****ing idiot given how badly we've already seen them **** up, together with how they've managed to write a headline that says nothing useful, before I'd start making claims of a conspiracy.