Anchored by Jake Tapper, The Lead airs at 4 p.m. ET on CNN.
We've moved! Come join us at our new show page.
Officials will spend the next few weeks, even months, combing through every detail of the Boston case looking for all possible missed signals that could have prevented this terrorist attack.
Former Connecticut senator Joe Lieberman knows the process well. While chairman of the Senate Homeland Security Committee in 2011, he and ranking member Sen. Susan Collins (R-Maine) put together a report on the Fort Hood shooting, when army psychiatrist Maj. Nidal Hasan went on a deadly shooting spree on a Texas military base, killing 13 people in 2009.
Lieberman has been asked to testify at next week's House Homeland Security hearing on the Boston attack.
Lieberman's report on Fort Hood and the lessons learned was released in February 2011, and states: "The FBI's transformation to become an efficient and effective intelligence-driven organization focusing on preventing domestic terrorist attacks is unfinished."
That was two years ago. After the events in Boston, it would seem the FBI's work is still unfinished.
"Since 9/11, there's been tremendous progress made within the FBI to become a first-rate domestic counterintelligence, counterterrorism agency," said Lieberman. "But mistakes were made in the Fort Hood Nidal Hasan case, and obviously were made here, too."
In the Fort Hood case, the FBI had evidence that Hasan was communicating by e-mail with the radical cleric in Yemen, Anwar al-Awlaki.
"It somehow got lost in the system and never got to the Army, so that the Army might have taken action against Hasan before he was able to kill 13 people at Fort Hood," said Lieberman.
Lieberman said in the Boston case, the FBI's 2011 questioning of suspect Tamerlan Tsarnaev should be revisited to determine if more could have been done.
The FBI will have to ask itself many questions, including, said Lieberman, "Did they convey information about him to the Joint Terrorism Task Force, on which Massachusetts state and local police would have been present? And of course, most of all, what happened when he left for Dagestan and came back and the Department of Homeland Security knew that, or at least the system showed it pinged as Secretary Napolitano said?"
"Why didn't they go back and investigate?" asked Lieberman.
"It's in everybody's interest, most of all the FBI, to go back and fix what went wrong in this case," said the former senator.
Former Attorney General Michael Mukasey recently wrote there have been five individuals questioned by the FBI who, after they were questioned, went on to commit terrorist attacks. Nidal Hasan is one of them. Tamerlan Tsarnaev is another.
"The kind of attack that occurred in, at the Boston Marathon is the kind a lot of us had nightmares about. We stopped a lot of terrorist attacks with tremendous help from the FBI, from the Department of Homeland Security, from the CIA," said Lieberman. "This one got through."
"We just have to go back and, in a very un-defensive way, figure out what went wrong ... and make sure that this kind of attack never happens again," said Lieberman.
Wednesday's arrest of three new suspects in the Boston case shows that this continues to be "a very hot investigation," said Lieberman.
"Anybody who made a conclusion early on that these were two lone wolves or they were acting in a primitive way, wrong. The more we go on, the investigation goes on, the more we learn. And I think everybody ought to just hold their conclusions until this process is over," said Lieberman.