The Boston Marathon bombing is another example of the US intelligence community knowing about the danger. The Russians rang us up and said "hey these two traveled to and from a known terrorist training camp", and everyone just shrugged.

Day-of, the bomb sniffing dogs left the finish line area when the VIPs did.

Not long after, the bombers set up their bombs...

speaking of shooting, not a single thing changed because no evident the sugested changes would help