I asked a friend who owns and has raced an M5 about this. A few comments:
1. The M5 is about the easiest of the "supercars" to drive. It has no bad habits up to the speed limiter, which kicks in around 155 mph. Though an 18-years-old kid's bad habits are likely to kick in sooner...
2. The current M5 is much more powerful than the older ones. The speed limiter is easily bypassed and the car will do 200mph.
3. He wonders if the kid tried some stunt from one of the "Crazy Arab" YouTube videos. An M5 won't do that and at 140 mph a launch & spin is easy to see.
4. 1.5 miles of pavement may seem like a lot but it isn't at 140 mph.
5. The kid may have started at one end and gunned it to 120 mph before hitting the brakes, then realized there was a lot of pavement left. Start at the other end and hit the brakes at 140 mph ... and he's egged on to try it again. This time he gets to 150 mph, hits the brakes ... and nothing happens because the brakes are hot and he launches off the end of the runway.
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"If they can't picture me with a knife, forcing them to strip in an alley, I don't want any part of it. It's humiliating." - windsock