The Boston Marathon will be held one week from today, and it will be the first since the bombing last year. As the one year anniversary of the tragedy approaches, Martha MacCallum looked back at what went wrong.

In 2009, Boston bombing suspect Tamerlan Tsarnaev was arrested in Cambridge, Mass., on domestic assault and battery charges, which were later dropped. Two years later, Russians sent a foreboding letter to the FBI, warning them of Tsarnaev.

The FBI Joint Terrorism Task Force opened a formal assessment, landing him on the first of several federal watch lists. Months later, Russians sent a second letter to the CIA, saying he was associating with radical Chechens, but the investigation into Tsarnaev was complete and the file was closed.

He was on four watch lists and databases, but still managed to buy a ticket and travel to Dagestan in November 2011, where lawmakers say he met with insurgents.

After the second letter from Russia, authorities ramped up an alert on Tsarnaev. If he were to try to travel somewhere, it was mandatory that he be stopped and turned over to authorities. None of this was shared with Boston police.

One of the reasons that he was able to travel to Russia and back was because his name was misspelled in the database by one letter. He was not detained on either leg of his journey.

Former CIA Director Gen. Michael Hayden admits that the system is not perfect.

MacCallum pointed out that when you improperly spell Tsarnaev’s name in a Google search, Google corrects it.

“Shame on us that we don’t have something that’s as good as Eric Schmidt has for Google,” Hayden said.

Rep. Mike McCaul said the bombing suspect came back from Russia a very different, more radicalized person.

Tsarnaev drew attention at a Cambridge mosque where he lashed out twice for sermons that he deemed too westernized. The FBI never questioned anyone at the mosque about him.

“We just have to step back and understand, in a country as large, as complex and as welcoming as ours, with a political culture that deeply respects free speech and privacy, from time to time, in the best of circumstances, with everyone doing everything right, some bad things are gonna happen,” Hayden said. “That’s just the way it is.”

Watch MacCallum's report above.