We are used to trials where evidence is neatly presented. I believe they had good reason to go in the house and it is promising that they carried out evidence. If they knew each other somehow, ML could have been to that house before. If so, finding her DNA or something of hers may not lead to arrest right now. They may have to sift through a bunch of potential evidence to decipher what is relevant. However, once any burn fragments (if any) or other evidence has been sent through a lab, the totality of the evidence will help law enforcement know what happened. I believe it is good they are taking appropriate steps before acting. The POI is on guard now and will be watched. If he did it, in desperation, he may lead them to more evidence in attempts to cover his track. We do not know enough to know how/if he is involved but we do know the LE knows enough to think so. I am not concerned at all that an arrest was not made. I do not believe that means no progress. In 4 to 5 days, I might think differently but not now.
Again, my heart is with her family and friends. This must be agonizing for them. My prayers go out to them. My heart is also with LE. Cases like this impact a person for a lifetime.