Originally Posted by BenKenobi
Vader was able to do this through the view screen in Empire so of coarse he could. However, it's a stretch to say he was on another level of the prison and was able to do it at the exact right moment. Not to mention the show reframes from directly making the Palpatine/Sidious reveal for whatever reason. Anyway, it's most likely Barris:
Palpatine was able to cloud the entire Jedi Order's force abilities. I'd say he is powerful enough to sense out what is going on in another room. Force choking someone at the right moment from somewhere else would be a cake walk for him. And let's not forget that the 501st that work the prison are in his pocket as is Tarkin. I'd say Palpatine can get anything done in that facility that he wants.
It could be Barris, but Palpatine is equally as likely.
Something else, the rogue Jedi could be tracing and listening in on all communications Barris is sending out to Ashoka. The rogue may have heard Barris telling Ashoka to go to the warehouse, and just went there also to further implicate her. Barris could still be innocent.