Perhaps not a machine — but something akin to a wheelbarrow? Granted, even that seems far fetched.

[No footprints. No hints as to what this is. Great. How big, exactly, are the marks though?]

Elizabeth mentioned a female did... well, this. [The double murder.] If we eliminate the two of us, that would leave Ava, Rose, Alice and, I suppose, Judy.

[Though she doubts it was Alice.]