This is what I think. They realized who the owner of the car was, I assumed it couldn’t possibly have anything to do with this particular family, and then let it go.
Note the message LE gave the other day doesn't mention the year, color or make of the car, they only ask that people submit information about who might have been driving it that day between 12 noon and 5 pm
Indiana State Police Release New Sketch, Audio, And Video In Investigation Of 2017 Murders Of Libby German And Abby Williams
For LE to know about this car, it's description and location would have been entered in police reports. There would have Yet LE doesn't give a any description of the car, none at all. Doesn't that indicate that LE assumes someone out there already knows the description of car that was parked at the lot and who owned it? How else could total strangers know which car LE is referring to? That message from LE was sent specifically to the owners of the vehicle and they know who they are.
I'm also wondering if LE saw this vehicle report early on, checked it out and said to themselves "Oh, that's so-and-so's car. They wouldn't be involved in this." Now they're backtracking. I'm kind of on board with the perp being someone who is related to or is a well known person in the community, or at least someone familiar and trusted by LE.
JMO