WASHINGTON — The House select committee investigating the Jan. 6 attack on the Capitol is increasingly focused on law enforcement failures that preceded the insurrection, scrutinizing in particular multiple warnings of possible violence that went unheeded by the FBI, according to people familiar with its work and individuals who have been contacted by the committee.

Donell Harvin, the former head of intelligence for the District of Columbia’s homeland security department, said he has met twice in the past two weeks with committee investigators, who he said appeared intent on understanding how information was shared between agencies in the weeks before the attack.

Harvin — whose team was in charge of assessing threats to D.C. — said he told committee investigators that he did not learn of the warnings received by the FBI in advance of Jan. 6 until months after the Capitol siege. “I told them that I think there needs to be a big discussion about how we look at domestic intelligence, because right now, it’s fragmented,” he said.

Harvin is among a half-dozen people familiar with law enforcement actions before the attack who have been contacted in recent weeks by the committee.

The interviews indicate that along with efforts to assess the role of President Donald Trump and his allies in spurring on the mob, the panel is pursuing a significant review of the intelligence and national security failures that is similar to the one undertaken by the 9/11 Commission in the wake of the 2001 terrorist attacks.

The committee is examining the failures of various government agencies to recognize, share and elevate critical early warnings of extremists discussing violence in the run-up to Jan. 6, according to two people familiar with the panel’s work, who spoke on the condition of anonymity to describe the investigation.

A spokesman for the select committee declined to comment. Rep. Bennie Thompson, D-Miss., serves as chairman of the panel, and Rep. Liz Cheney, R-Wyo., serves as vice chair. The FBI did not comment.

The committee’s examination of some specific red flags that preceded the Capitol attack follows a Washington Post investigative series published late last month on the causes, costs and aftermath of Jan. 6. The series revealed that the FBI and other federal agencies did not respond with urgency to a cascade of warnings that Trump supporters were planning mayhem in Washington that day.

Internal FBI documents obtained by The Post showed that the bureau received tips that people were making plans online to travel to D.C. and overrun police, and that some were threatening lawmakers with public trials and violence.

The documents show a bureau official sought to classify one set of warnings in December as a domestic terrorism issue. But the threat assessment was closed within 48 hours and passed along to D.C. police and the Capitol Police with a notation, “Does not warrant further investigation at this time.”

FBI officials told The Post that much of the alarming chatter online was “aspirational” and protected free speech, and defended the bureau’s work as proactive and aggressive.

The House select committee has been pressing the FBI to turn over additional documents related to the bureau’s handling of Jan. 6, frustrated that it has not yet received more material, according to people familiar with the matter who spoke on the condition of anonymity because they were not authorized to do so publicly.

It is not unusual for tensions to develop between congressional committees and national security agencies over document requests, and officials said the two sides are discussing paths forward.

Meanwhile, committee staff have contacted numerous officials familiar with the work of the FBI and other federal agencies, including Washington Mayor Muriel Bowser, D, and Christopher Rodriguez, the head of the District of Columbia’s homeland security agency. Those two are expected to meet with committee staff soon, according to people familiar with the discussions. Mike Sena, the president of an association of the nation’s regional homeland security offices — known as fusion centers — said he has also been in touch with the committee.

The Post series detailed how D.C. and fusion center officials sought to warn federal agencies of alarming intelligence related to Jan. 6. The committee is seeking to review how every agency identified as receiving such information then processed and handled those alerts.

One area of focus for the panel is the FBI’s reluctance to formally investigate outspoken Trump supporters after classifying many online discussions about Jan. 6 violence as First Amendment-protected speech.

Some documents the committee seeks relate to the bureau’s handling of alerts about what members of far-right groups were plotting, including coming to D.C. armed, being willing to shoot police officers and targeting lawmakers for arrest, one person said.

Other documents that the committee seeks pertain to how the FBI reviewed those and other warnings from a multitude of sources, and then reached decisions not to more thoroughly investigatethem, said the person familiar with the committee’s work.

The committee is negotiating with the FBI about obtaining information from these records in some form, most likely with redactions, to address concerns that releasing the records could reveal or compromise sensitive investigative sources and methods.

Another area of concern is how information was treated that flowed to the FBI from the nation’s network of fusion centers, an infrastructure created with grant money from the Department of Homeland Security in the wake of 9/11. The centers are charged with assessing open-source information and sharing tips to help interrupt planning for attacks before they occur.

Harvin’s fusion center team was so concerned by social media posts indicating that extremists were coordinating to meet in D.C. that he and others briefed counterparts from nearly all 80 fusion centers in a rare, nationwide conference call on Jan. 4. On the same day, Harvinurged D.C.-area hospitals to begin preparing for a mass-casualty event.

The FBI had a liaison assigned to Harvin’s office, but it is not clear what the bureau did with the information that flowed from that network.

In the week before Jan. 6, the FBI’s ability to analyze online chatter itself was hampered when agents lost access to Dataminr, a monitoring system they had used to keep tabs on the frequency that certain key words and phrases are used on the Internet, as The Post series reported. In a previously planned transition, the bureau moved to a new monitoring service at the beginning of 2021, but many agents had not yet been trained on how to use it.

The people familiar with the committee’s work said lawmakers may include a section of their eventualreport on how to improve the process for intelligence sharing and assessing threat intelligence, with an emphasis on the FBI.

Rep. Adam Schiff, D-Calif., a member of the committee, said assessing the state of intelligence before the attack is a key part of its mission.

“It is our job to write a set of recommendations like the 9/11 Commission did,” Schiff said, noting that that effort led to restructuring of the nation’s intelligence agencies. “I don’t know if we should expect something as dramatic and profound as that but we’ll make our recommendations based on the evidence that we find.”

The committee has also been looking at how Trump’s effort to subvert the results of the election led to pressure on officials around the country.

Maricopa County Supervisor Clint Hickman, a Republican who faced political backlash and threats after voting to certify President Biden’s victory in his county, said he was interviewed by two staffers from the committee at his Phoenix office for about 45 minutes on Nov. 17.

Hickman, who was also featured in The Post series, said the committee staffers were interested in two phone calls he received from the White House in the days just before the attack on the Capitol. He did not return either call, but said that he believed that had he answered, Trump would have pressured him to try to find a way to undo Biden’s win.

The committee staff also asked him about threats he has received since the election, including his experiences on Jan. 6, when local sheriff’s deputies evacuated him and his family from his suburban Phoenix home in fear that the violence in D.C. could spread to his community, Hickman said.

The Washington Post’s Jacqueline Alemany, Devlin Barrett and Rosalind S. Helderman contributed to this report.