PinkSushi, I grew up in Manoa Valley, lived there for 65 years, and hiked the trail MANY times.  As kids, we used to take our bikes up that trail, too.  It was like my back yard.  There are many steep drops on the way to the falls, and even at the falls themselves, it's possible to tumble 30 feet off the higher parts of the trail and large boulders to the lower parts of the stream.  All my previous statements are FACT, but you still promote unfounded assumptions: "the trail is flat all the way... he didn't slip on a wet trail... go into a kapu... area..."  are purely assumptions made by YOU.  You say nothing of being there to witness the accident, so I assume you weren't.  Correct?