It’s because in the warrant, it’s been specifically stated that investigators believe the older two Dedmon girls were involved but needed adult assistance to execute/cover up the crime.
I have seen that interpretation of the meaning of the search warrant before, but I don't agree that is what it means.
I believe that language has a legal purpose, to explain in a nueutral/legal/universal fashion why evidence pointing to involvement of a child or children, is a still a legally proper basis for police to search and seize evidence from their parents.
IMO, police just write a search warrant to cover all their bases, in case it leads, eventually, to a court case where the relevance/validity of the search warrant could be challenged by some future defense attorney.
In particular, a defense attorney might challenge the search warrant, and try to get it thrown out of court, on the basis that the hair of a then 13 year old girl, was not justification to search her parents homes. So the police/lawyer who wrote up the search warrant threw in the comment that, even IF a child/children was involved, that still justifies the search warrant.
The purpose of the search warrant is to convince a judge it's lawful to seize private property, not to spell out any current theories or 'beliefs' of police. Just because police 'believe' something, is not justification for a warrant. They have to have evidence.
There's no evidence except the hair, the other DNA, and a witness statement about a (potentially quite different model) green car.
How could those thing possibly cause police to go off on a wild theory about what actually happened, involving the daughters?
My understanding of modern police methods is that they avoid developing any theory, since that just leads to tunnel vision and missing/ignoring key evidence because it doesn't match the fixed belief of what happened.
JMO