Technically yes you can say the police failed and River wasn't at fault. Specially if as you've said before (if true) that the whole operation of giving the bus protection was more relaxed than usual. But here is my view. If I am River, and as it had been speculated for weeks that this was going to be WW3, and everybody was worried about how the city would deal with the rivalry, I would coordinate with police to see what their plans were. I would ask for even more security since this is a Libertadores final and emotions are even more heightened. It's in River's best interest that everything goes smooth. They should show that they went above and beyond to ensure all or most risks are accounted for. So for me, the fact that it wasn't their responsibility to monitor outside the stadium doesn't take blame away from them. If there was less security than usual and they didn't know, that's their fault as well. Unless they were lied to. You may respond by saying Boca acted the same way. But that's life. You only get screwed when something goes wrong.