Maybe a compelling, recent witness' statement contradicts previous witness statements?
Maybe, but it seemed more like they want to know who E & X may have talked to, interacted with in any way (face to face, via text, etc). Seems like they know where E & X were, when they were there, and generally what they were doing, but are now looking for any sort of interaction or event they're unaware of. I just can't imagine they don't have X & E's cell phone data yet, assuming they do, they know who they called, who they texted, what they said, and where they were and for how long...
It almost seems like LE is looking for something almost random (probably wrong word but best i can do atm), seemingly innocuous or innocent anything that could connect X & E or the house to the killer because they haven't been able to identify anything related to K & M.
I think they have a much more specific footprint of K & M's night than they have for X & E, probably because K & M were places with cameras (the food truck, the bar, cameras in businesses and on houses that K & M may have passed to and from places, etc). Because X & E were at a frat party, then home, then quick food run, they have a lot less specifics and a lot less camera footage.
Maybe I'm reading too much into it, but when I saw the direct statements about X & E's timeline gaps, my heart sunk, because it just seems like they thought they were going to find something with K & M and haven't and now need minutia on the two other potential targets.