Let's just say that LE are getting ready to compile an arrest warrant (my big hope is that this is true).
SPECULATIVE ARREST SCENARIO
If they do suspect that a certain person, using a particular car, was involved in this crime, they'd want a stack of evidence t present to the judge. Let's just say the DNA results are not in yet, so what can they get?
First, they almost certainly have cell tower information from 3-4 cell towers in the area, showing whose phones were active in the area on the night of the murders. Figuring out this web of data was probably someone's full time job for the past couple of weeks. They cross-tabulated the cell tower data with various known person's whereabouts (including the victims, but also their friends and family). Perhaps one person thought to have been in the area did NOT have cell phone data showing him out and about, therefore arousing suspicion. They then subpoenaed that person's cell records, which show that usually, he has his phone all the time, uses it frequently, but was mysteriously absent from his phone for a time period on the night of the murders.
Second, that person (already spoken to early on) has now left the community and is not with his parents (if relevant).
Third, that person had a known connection to the house, and phone data show that he'd been there before. LE probably have a few phone numbers where they've subpoenaed data. These would be subpoenas that are kept off-record for the present.
Fourth, a Hyundai drives by the house but none of the cell tower data show a phone that relates in any way to a Hyundai - so there's a "quiet" car for whom no cell data is available. LE probably called every single number provided by the cellular provider for several cell towers, revolving around who was awake and using their phones on that evening, within a certain radius. Perhaps the Hyundai is revealed on other security tape to have obscured its license plate (as suggested by Otto). They sell covers for license plates that make it impossible to pick the plate up on cameras (these are illegal in many states, but that was irrelevant to the mind of the killer). I see these all the time here in Cali. That makes the driver/owner suspicious in my view - and in the view of LE.
Fifth, they have interviewed this person and there were consistencies. The term "POI" is hardly ever used any more. The man charged with the Delphi murders went, to my knowledge, from regular person to arrestee without any terms about POI or suspects.
Is this enough? For an arrest? What do you think? I think there's probably more, hopefully there's more (texts showing unwanted contact with house members or disagreements; etc. IOW, some glimmer of motive.
If the Quiet Hyundai, as I'm calling it, is obtained and contains the DNA of this suspect, they can place him AT the scene at the relevant time (of course, he'll claim he was in the car at some other time - he can go to court with that). But if it's his actual car and they can show it had cruised by the house on multiple occasions, that would be persuasive to a jury. IMO.
I'm sure you all can add to this and say whether you think this is "enough" or not. It would be really awesome if the jacket shown in an early Foxnews video (and posted on Yahoo news) turned out to play a role here. A long shot, IMO.