If you don't mind sharing, what was the reason to get in the car with them to drive? Were you planning to head out to an event like a hike or something that you had arranged online, but hadn't known the people ahead of?
I was visiting a college town for an away football game. This was the night before the game and some of my friends and I went out. I met these two guys at a college bar my friends and I went to. My friends were going back to our hotel but these guys (who we had all met maybe an hour before) had invited me to a party. It was still fairly early and I thought "Neat, this will be a different and interesting experience". Unfortunately it was - much more than I had imagined.
It's likely that if the circumstances were closer to what you've described the police would have taken me more seriously.
I should also probably add that this was in a period of my life where I was unknowingly experiencing untreated bipolar disorder. If you're not familiar with manic or even hypomanic episodes your risk assessment can be very warped. That was a large component of this situation.
In my situation the bar was a corporate national chain in the downtown center with locations in most college towns (at least in my experience). They likely had video surveillance from every angle. The perpetrators may have even paid by credit card, been already known to others there, possibly even the staff, etc. Compared to the situation your friend's brother experienced it seems like there's a decent chance my assailants could be caught. As I said I'd been talking to them for an hour, left with them, etc. Video wouldn't be tough to get.
I often wonder if it was a one-off crime of opportunity or some MO/pattern of theirs. No way to know I suppose but given my case they certainly wouldn't have any reason not to do it again.
I feel bad that my inability to deal with this could contribute to it happening to someone else. But, certainly at that time, I just couldn’t bring myself to even talk about it.
Oddly, years later, I can talk about it on HN and think nothing of it. Occasionally my friends will have me tell the story to someone else and we’ll all laugh about it (occasionally to the horror of anyone hearing it for the first time).
It’s been a very strange experience.
"Comedy is tragedy plus time."