I think you are correct. If any human remains had been found it would have been enough to keep him in custody.
Once arrested the clock immediately starts ticking. It's better to wait, and get it right rather than rushing.
Imo, since they are calling him a POI, and had enough probable cause to execute the warrants I think it's just a matter of time.
Imo, they have him under surveillance.
If they found any remains or what appears to be human remains such as loose teeth, charred bone fragments, etc. they will wait until DNA testing is completed so the victim can be positively identified.
They can't arrested him for murder until they identify irrefutably who the victim is by naming the victim on the charging indictment.
They can't assume who most likely is the victim. It must be confirmed.
They may have found what they believe to be more than one victim.
Prosecutors have three elements they must prove in all murder cases.
1. The positive identity of the victim or victims.
2. Their death was due to homicide..such as homicidal violence.
3. The accused is guilty BARD.
I don't think they have all of those required elements known to them yet.
Jmhoo