Might just be the oxys talking here, but I have considered the whole crime scene from the angle of being a 'water burial', which I believe it was actually described as, by somebody or other.
My perspective on the theory that the nudity and clothes poked into the water was a means of removing DNA is that I would expect this behaviour form a man who knows what perils leaving one's DNA around might bring, somebody familiar with the cost of that..
I have hard time seeing a bunch of feral, drunk teenagers, or indeed anyone who hasn't been arrested for like crimes, having that much forethought after committing the heinous triple murder of three kids.
Murder is stressful (so I hear..) and exhausting, or exhilarating, depending on how sick a person is. That's why so many one-time killers get caught at it - they are all over place afterward, they are sloppy and make mistakes.
But this killer (or killers) -didn't- make any mistakes, if that was the reason for the boys going into the water.
If there wasn't a practical reason like that, and I can't discount that possibility, then I see the bindings as maybe a sick aesthetic, something memorable for, or meaningful to, the perp.
I am reminded of the way JKM described (in some detail, pass the eye bleach) the majority of pedos preferring not to commit anal rape, as it's too hard to get rid of evidence, and thus find it better to commit non-penetrative sexual assault.
He also said a pedo might kill if one of the boys looked like he was going to tell.
In my research, and via conversations with various prison guards, I learned that violent pedos are more likely to kill a victim if they have been incarcerated for a prior crime.
Just food for thought.