Did the Boston Marathon Bombers Have Terror Training?

New Court Filing Echoes Suspicions From Top Experts, Officials
2:09 | 05/22/14

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Transcript for Did the Boston Marathon Bombers Have Terror Training?
New court documents are reigniting that question were those two Brothers acting alone during the Boston bombings or did they in fact get help. And there's something else tonight why the lack of gun powder found in their car could be a powerful clue. Back on the case tonight ABC's chief investigative correspondent Brian Ross. Until now the FBI had maintained only two people were responsible for the deadly marathon bombs the tools are not half Brothers -- and killed in the shoot out later and Joseph -- now awaiting trial. But as ABC news has reported the marathon bombs were surprisingly sophisticated. And in court documents filed this week the government admitted it would have been difficult for those are not adds to fabricate successfully without training or access from others. For them be as successful as they were -- they did some training and somewhere and then they did some sort of folk practices. It was very well planned and very well executed. The government says searches of his -- homes and cars found no evidence of gunpowder. Quote suggesting that others had -- or at least helped us -- I have spilled the bop its officials do know the elders -- -- I have traveled to meet with Chechen rebels a year before the attack. But congressional investigators say the FBI failed to fully follow up on that connection do you think it -- we -- second would just maybe we could could stop this. Adding to the concerns of some foreign terror involving. The government now says with the full text abruptly younger brother wrote. As he hid from police in that -- scrawled on the wall of the -- and obscured by four bullet holes as seen in this photo obtained by ABC news our writings the government says bear the hallmarks of al-Qaeda. Quote no you are fighting men who look into the barrel of your gun and see heaven stop killing our innocent people and we will stop. Congressman McCall has called for a further investigation into whether others were involved in this country or overseas and helping the accused Boston bombers but for the moment. Officials inside the FBI say it all leads have been exhausted with no other suspects identified at this point it was all right Brian Ross tonight thank you.

This transcript has been automatically generated and may not be 100% accurate.

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