The FBI is stonewalling a congressional investigation into intelligence failures, the chairman of the House Homeland Security Committee complained today at a hearing looking into the Boston Marathon bombings and several other domestic terrorism assaults.

“I walked the streets of Boston with my colleague (U.S. Rep.) Bill Keating, and while the city’s resilience and strength were obvious everywhere we went, how this attack could have occurred in spite of multiple warnings was still not clear,” said Chairman Michael McCaul, R-Texas.

The Republican chairman acknowledged the public start of Dzhokhar Tsarnaev’s trial with his arraignment in Boston’s U.S. District Court today and said his committee would begin hearing classified testimony tomorrow in a closed session with the federal Department of Homeland Security and officials from the National Counterterrorism Center. But he panned FBI officials for refusing to come forward.

“The FBI has refused to appear and continues to refuse this committee’s appropriate requests for information and documents crucial to our investigation into what happened in Boston,” McCaul said. “The problem at the heart of preventing the Boston bombings — the failure to share information — is being witnessed now in this very room. The information requested by this committee belongs to the American people. It does not belong solely to the FBI.”

Speaking at the hearing in Washington today, Boston Police Commissioner Edward F. Davis said while federal, state and local cops worked well together following the bombings, “there is a gap with information sharing at a higher level while there are still opportunities to intervene in the planning of these terrorist events” and he suggested changes in the agreement for joint federal-state task forces.

“Information sharing with local law enforcement task force members need to be improved,” Davis said. “In the aftermath of the marathon bombings, the FBI improved information sharing. This sharing needs to continue and be consistent across all joint terrorism task forces.”

Davis said Boston officials learned from attacks on other cities worldwide and he plans to visit the Middle East this year. “My experience with authorities from London, Northern Ireland, Israel and Jordan was critical to an understanding of what was happening on April 15, 2013.”

Mirroring problems at Ground Zero on 9/11, Davis said law-enforcement officials need a common bandwidth for their exclusive use as the city’s cellphone system was quickly overwhelmed. He hopes for more cameras as well, all problems that will require assistance from the federal government, he said.

The bombings served as a report card on the nation’s counterterrorism efforts 10 years after 9/11, McCaul said, demonstrating that clues can be lost when anti-terrorism agencies fail to share information.

“Terrorists within the U.S. who are inspired by jihadist rhetoric present a new and dynamic threat and must not be looked at as any less deadly that those abroad ,” McCaul said. “In light of Boston, it is more important that ever to find weaknesses in our counterterror efforts that can be fixed before another attack is attempted.”