Edited based on the events of Episode 9 In the 8th episode of Westworld, it was reveled in a split-second flashback that Bernard had killed other people for Ford before - and many people believed the flashback showed Elsie being strangled.
It was reasonable to think that that could happen because Elsie told Bernard about her discovery and where she was going.
Then Episode 9 explicitly showed Bernard strangling Elsie.
However, in the episode where Elsie first went missing, she was just talking on the phone with Bernard. The abandoned theater where Elsie went missing is presumably miles away from where Bernard and Theresa were in that time, across the park.
So how is it that Bernard reached Elsie? Is there an in-show explanation, is it information we do not have, is it a plothole? Clearly he covered an extremely large distance in an extremely short time, and Ford was never present to help him at the theater.