Apart from the FBI likely getting inundated by tips and leads on a daily basis, I am at a loss to think how this could be stopped. The only way this could have been stopped is if there were 24 hour a day surveillence on the two bombers. I am sure with the amount of tips they have, there just aren't enough resources. Then there are so many laws which gives terrorist suspects rights. The do gooders of society ensure this.
Now the blame game begins. I don't know how law enforcement are able to spot a terrorist carrying a backpack in a crowded area. Nearly everyone would have had a backpack and these guys would just easily blend in with the rest of the crowd. Unfortunately, people are always going to fly under the radar and leads are always going to be missed.
