I wonder if the FBI will get a warrant to place a GPS tracker on the family car. Hopefully they now have evidence that they've aided and abetted their son.
Knowing what they bought that might be out of place for a couple living in their home could be more than useful because we know they're secretive and may have ways of getting things to him. I wouldn't trust them at all.
I would bet almost certainly there is GPS tracking on all the vehicles, including relatives. And that there is 24/7 video surveillance on the parents' home via help of cooperative neighbors. Possibly also audio surveillance within the home too or gathering enough evidence via other means in order to obtain a sealed warrant to do so. The very visible foot and car surveillance is probably mostly to maintain pressure on the parents...constant reminder that their lives will never be the same, the USG will never give up, and the parents and Brian will eventually have justice served.
just my opinion.