Anchored by Jake Tapper, The Lead airs at 4 p.m. ET on CNN.
The latest news on the crisis in Ukraine, plus a look at the technology aiding in search for Flight 370.
A growing sentiment among Republican lawmakers is that the Boston Marathon bombing suspects did not act alone. They made the rounds on the Sunday talk shows, saying they believe Tamerlan and Dzhokhar Tsarnaev are part of a bigger terrorist plot. They believe the brothers had foreign help with training, or that a radical group may have pitched in to help finance the attack.
The circuitry of the bombs carry a certain signature that will help investigators uncover how the plot came together, said CNN contributor and former CIA operative Robert Baer.
Multiple reports indicate "the police are looking at this as a sophisticated device, which does not precisely follow the internet plans that are in "Inspire" magazine," said Baer, referring to al Qaeda's affiliate in Yemen's online English language magazine. "If that's the case, there's a master bomber out there."
The question is whether the mastermind is overseas, like in Dagestan, or in the United States.
"If he's in the United States, there's a chance he could strike again," said Baer. "I'm waiting for an FBI agent to step forward ... and tell me just how sophisticated this thing was."
Last week, a Boston cab driver told "The Lead" that he picked up the Tsarnaev brothers the day before the attacks, and that the suspects both had heavy backpacks with them.
"I think they were either out there practicing with the firing devices, or they picked them up from somebody," said Baer. "If they made them off the internet in their kitchens, they wouldn't be carrying them in rural Massachusetts, outside of town, it just doesn't make sense."
In his 35 years of experience, Baer said it is very difficult to detonate these bombs. In an attack like the one at the Boston Marathon, the last thing the terrorists want is the bomb to be a dud, because the plot is then uncovered and everyone goes to jail.
"In order to have them foolproof, you need a bomb maker to do it, or someone with a lot of practice," said Baer.
"These things just don't go off with that consistency that they managed to make happen."