EDIT: instead of rejecting the Taliban's offer outright and, say, negotiating and acceptable outcome, we chose to go to war, spend trillions of dollars, kill countless people and ultimately still leave the Taliban in power.
The Taliban saying they need proof is a negotiation. There is no court of law. We could've simply bribed them. Imagine how much cheaper and how many lives would've been saved if we'd simply given them $1 billion to hand over bin Laden.
But no, instead we started a war we could never possibly win. And again, that's not hindisght being 20/20. The US has not won a war since 1945. We watched the USSR, who had far more tolerance for losses, lose a war in Afghanistan. Like in what world did we think we would ever "win"? The outcome was entirely predictable and foreseeable. Irony of ironies, it was our material support to Afghanistan in the Soviet invasion that quite literally created bin Laden.