In my opinion, they got forensics that indicated something of interest in the 1st floor rooms, which sent them back for another look - this time with luminol. They likely wouldn't have tested the 1st floor rooms for blood before now, as the theory was no involvement there. Just my opinion. Doesn't mean the 1st floor survivors were involved, could be a houseguest they had overnight, etc. MOO. The fact they left the house with samples would indicate to me they got a hit on the luminol and took the splatters for further testing. Seems an ominous development, in my opinion.