FBI informants generally have day jobs. His religion is of little relevance.
Apparently locals say the intersection was "accident-prone". What that means is not clear, based on news reports, but some intersections are pretty dangerous. That can be because of the volume or type of traffic they serve, but can also be due to weaknesses in design. I've lived beside one that regularly invited near-fatal collisions (usually on Saturday night, in the middle of SNL) and regularly pass through some where stop signs are overgrown or it is difficult to see oncoming traffic because of posts, hedges, and such.
Personally, I don't know what the hell a stretch limo is doing with a seating capacity of 19, including driver. Eight and a driver, fine - many minivans will do that - but 18? That's a bus. You also have to wonder what such a large number of boisterous people in a car does with respect to potentially distracting the driver. I'm certainly not blaming the victims, nor absolving the driver, but there are a whole lot of factors at play here, and a large number of decision points that make one want to ask "Why in the hell would you actually DO that?".
But like I said, a lot of misery begins with "I'm just gonna...". Humans are not great judges of probability. So much tragedy results. So much.