Unfortunately the courts have repeated ruled that "aware of the Constitutional violation" means knowing that the exact action being observed had previously been ruled a violation of Constitutional rights. It's essentially impossible to prove, which is one of the reasons we don't see that offense prosecuted.

In the Chauvin case all three of the bystanders were sent to prison by federal courts specifically for civil rights violations stemming from their failure to intervene as Derek Chauvin murdered George Floyd in front of them.