Remarkably large IF.
Nobody knows who murdered the little princes. The theory that Henry VII did it is based on the highly unlikely theory that Richard III would keep them locked up incommunicado as his support eroded because of suspicion he'd bumped them off.
It's fiction, and therefore can be constructed to prove anything.
Second-guessing history is an amusing pastime, but no more than that.
You make a good point re: Richard III keeping the princes locked up while public opinion turned against him. If he didn't do it, somebody working for him did ("Will nobody rid me of this troublesome priest?")