WASHINGTON — Federal Fusion Centers — massive data-retention facilities funded in part by the Department of Homeland Security — have spread out across 77 cities, collaborating with local law-enforcement agencies to identify and defuse terrorist threats.

But the center in Massachusetts, an early adopter of the intelligence-gathering program, failed to stop the two accused Boston Marathon bombers. Indeed, in the run-up to the attack, officials acknowledged that the left arm of the law didn’t know what the right arm was doing.

Testifying at the House Homeland Security Committee this month, Boston Police Commissioner Edward Davis said he was unaware that the FBI had, in 2011, questioned one of the brothers implicated in the deadly street bombing.

“In a literal sense, the homeland security system that we built after 9/11 to protect the American people from terrorist attacks failed to stop the Tsarnaev brothers,” Sen. Joseph Lieberman, I-Conn., told the panel.