Chico - NICS is not investigating this, they were there though because of the person that they questioned. It's military protocol to have them present when someone military is being detained and questioned. They're a scarey group too, because while local law enforcement shows up with a couple of detectives to question you - NCIS shows up with a team. They questioned me several years ago in relation to some robberies in North Chicago, myself and a friend of mine saw a young guy getting beat up, so we stopped to help him (we caught one of the guys and put him in the hospital the other ran off when the car stopped), turned out it was a couple guys that were pretty much beating and robbing new sailors that were going to the exchange. When NCIS came to visit me there were 5 of them, and I didn't do anything wrong

First and foremost it's the Portsmouth Police Department's jurisdiction, which can be federally overridden - normally by the FBI, but just because they're there, does not mean that they're the ones controlling the investigation. Beacuse of the area, there's a lot of interdepartmental cooperation required - more than you would ever think (more than I ever thought as well, but I know several people that work for and with the police departments in the area). There may be information sharing and you may see NCIS again if they take a suspect in custody that is military, but old standard is that civilian authorities get first crack at you. Also if someone is taken into custody, they'll be taken into custody of the Portsmouth Police. I'm sure there is a list of suspects that they're working through, but who knows how long it'll take. Also, since they said it's not random, there's not much need for the average person to be afraid, at least not of being the "next" victim. Be afraid because this sort of thing is becoming commonplace, but not that there's someone stalking victims.
I will agree, however, that there is someone walking around right now that given the right circumstances could very well become violent again. They need to be caught. I don't see, and I'm not hearing of anything that would cause further alarm.
Police departments (state, federal and local) tend to not release alot of information anymore, they work through one spokesperson that decides what to disseminate and what not to, which works out great because they tell everyone the same thing and there's not much variation to it at all.
As far as what federal law enforcement drive, you'd be surprised. They own a whole fleet full of Chrysler Vehicles, 300's, Intrepids, along with other siezed vehicles that were never released. They blend in pretty good to everyone else, which I would suppose is the intent.