What the FBI learned from the Boston Marathon bombing investigation

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BOSTON — It has been nearly six years now since the Boston Marathon bombing and we're learning the FBI says the terror threat remains strong.

Special Agent in Charge Joseph Bonavolonta is taking over the Boston office of the FBI just as this region marks the sixth anniversary of the Boston Marathon bombings.

"I can tell you sitting here today that we as the Boston division, are going to remain ultra focused on ensuring that any threats that may arise are going to be vetted out as much as humanly possible," Bonavolonta said.

In a one-on-one interview, he told Boston 25 News the investigation into the bombings and Brothers Dzokhar and Tamerlan Tsarnaev is over.

"As we sit here today, there is no more proactive investigative activities going on," Bonavolonta said. "The investigative portion of that case is closed."

Bonavolonta said the lessons learned from the Tsarnaev case -- how they radicalized themselves, how they stayed completely under the radar as they planned and carried out the attack -- have revealed the dangers of domestic terror.

And how timing is everything.

"The self-radicalization portion can go on for somewhat of a lengthy period of time," Bonavolonta said. "But between that period and actually going operational, it can sometimes be hours, or days at the most."

To fight back, he tells me the bureau is focused on building relationships with community and faith leaders to recognize a threat before its too late.

"We need the community and our partners to ensure they are remaining engaged with us, and us with them," Banavolonta said.