WASHINGTON — The FBI did not initially share with Boston police the warnings it had received from Russia about one suspect in last month's marathon bombings, despite the work of four city police representatives on a federal terrorism task force, Boston's police commissioner told Congress on Thursday.

Yet Commissioner Ed Davis acknowledged that police might not have uncovered or disrupted the plot even if they had fully investigated the family of Tamerlan Tsarnaev based on those warnings. The FBI after a cursory investigation closed its assessment on Tsarnaev, who died in a police shootout after the bombings. Boston police learned about the Russian security service warnings only later.

“That's very hard to say. We would certainly look at the information, we would certainly talk to the individual,” Davis said. “From the information I've received, the FBI did that, and they closed the case out. I can't say that I would have come to a different conclusion based upon the information that was known at that particular time.”

The congressional hearing was the first in a series to review the government's initial response to the attacks, ask what information authorities received about Tsarnaev and his brother before the bombings and consider whether everything was handled correctly.

Some lawmakers questioned whether Boston police could have more thoroughly investigated Tsarnaev after 2011, based on Russia's vague warnings then to the FBI and CIA or the discovery by the Homeland Security Department in 2012 that he was traveling to Russia for six months, and whether Justice Department rules intended to protect civil liberties constrained the FBI's own inquiry.

Davis' testimony revealed a gap in information-sharing between federal and local officials. That was somewhat reminiscent of intelligence failures that preceded the 2001 terror attacks.