And I would like to add: If drugs, suspicions of drugs are a contingency, DCF and LE does require drug testing, if they come back positive you don't retain custody of the kids. I can tell you names upon names just in my area of the households where dcf was involved and the parents are required to take drug tests. It's a common tool for DCF, not to mention the courts can and does enforce them upon granting child custody.
LE knows lots more than we do. Seems with the new investigators, we're getting more info on a regular basis. I believe they have their suspect or suspects and are gathering corroborating evidence in order to gain an arrest and make it stick, because Haleigh or her body has not been found, so the threshold for them is different than having Haleigh to move forward.
They arrested Caycee when they received corroborating evidence of the forensic testing of decomp that came back positive in the car, along with the cholorform and dead hair forensics.
If it is a family abduction, and Haleigh is safe and alive, if LE knows this, then it's a cat and mouse kind of investigation.