WASHINGTON (AP) — The Defense Department took more than three hours to dispatch the National Guard to the deadly riot at the U.S. Capitol after a request for reinforcement from police, according to testimony Wednesday that added to the finger-pointing about the government response.

Maj. Gen. William Walker, commanding general of the District of Columbia National Guard, will tell senators that the then-chief of the Capitol Police requested military support in a frantic 1:49 p.m. call, but the Defense Department's approval for that support was not relayed to him until after 5 p.m., according to prepared testimony. Guard troops who had been waiting on buses were then rushed to the Capitol.

The Senate hearing is the second about what went wrong on Jan. 6, with national security officials expected to face questions about missed intelligence and botched efforts to quickly gather National Guard troops that day as a violent mob laid siege to the U.S. Capitol.

Senators are eager to grill officials from the Pentagon, the National Guard and the Justice and Homeland Security departments about their preparations for Jan. 6. Supporters of then-President Donald Trump had talked online, in some cases openly, about gathering in Washington that day and interrupting the electoral count.

At a hearing last week, officials who were in charge of security at the Capitol blamed one another as well as federal law enforcement for their own lack of preparation as hundreds of rioters descended on the building, easily breached the security perimeter and eventually broke into the Capitol. Five people died as a result of the rioting.

So far, lawmakers conducting investigations have focused on failed efforts to gather and share intelligence about the insurrectionists’ planning before Jan. 6 and on the deliberations among officials about whether and when to call National Guard troops to protect Congress.

The officials at the hearing last week, including ousted Capitol Police Chief Steven Sund, gave conflicting accounts of those negotiations. Robert Contee, the acting chief of police for the Metropolitan Police Department, told senators he was “stunned” over the delayed response and said Sund was pleading with Army officials to deploy National Guard troops as the rioting rapidly escalated.

Senate Rules Committee Chair Amy Klobuchar, one of two Democratic senators who will preside over Wednesday's hearing, said in an interview Tuesday that she believes every moment counted as the National Guard decision was delayed and police officers outside the Capitol were beaten and injured by the rioters.

“Any minute that we lost, I need to know why,” Klobuchar said.

The hearing comes as thousands of National Guard troops are still patrolling the fenced-in Capitol and as multiple committees across Congress are launching investigations into mistakes made on Jan. 6. The probes are largely focused on security missteps and the origins of the extremism that led hundreds of Trump supporters to break through the doors and windows of the Capitol, hunt for lawmakers and temporarily stop the counting of electoral votes.

Congress has, for now, abandoned any examination of Trump’s role in the attack after the Senate acquitted him last month of inciting the riot by telling the supporters that morning to “fight like hell” to overturn his defeat.

As the Senate hears from the federal officials, acting Capitol Police Chief Yogananda Pittman will testify before a House panel that is also looking into how security failed. In a hearing last week before the same subcommittee, she conceded there were multiple levels of failures but denied that law enforcement failed to take seriously warnings of violence before the insurrection.

In the Senate, Klobuchar said there is particular interest in hearing from Walker, the commanding general of the D.C. National Guard, who was on the phone with Sund and the Department of the Army as the rioters first broke into the building. Contee, the D.C. police chief, was also on the call and told senators that the Army was initially reluctant to send troops.

“While I certainly understand the importance of both planning and public perception — the factors cited by the staff on the call — these issues become secondary when you are watching your employees, vastly outnumbered by a mob, being physically assaulted,” Contee said. He said he had quickly deployed his own officers and he was “shocked” that the National Guard “could not — or would not — do the same."

Contee said that Army staff said they were not refusing to send troops, but “did not like the optics of boots on the ground” at the Capitol.

Also testifying at the joint hearing of the Senate Rules Committee and the Senate Homeland Security and Governmental Affairs Committees are Robert Salesses of the Defense Department, Melissa Smislova of the Department of Homeland Security and Jill Sanborn of the FBI, all officials who oversee aspects of intelligence and security operations.

Lawmakers have grilled law enforcement officials about missed intelligence ahead of the attack, including a report from an FBI field office in Virginia that warned of online posts foreshadowing a “war” in Washington. Capitol Police leaders have said they were unaware of the report at the time, even though the FBI had forwarded it to the department.

Testifying before the Senate Judiciary Committee on Tuesday, FBI Director Christopher Wray said the report was disseminated though the FBI’s joint terrorism task force, discussed at a command post in Washington and posted on an internet portal available to other law enforcement agencies.

Though the information was raw and unverified and appeared aspirational in nature, Wray said, it was specific and concerning enough that “the smartest thing to do, the most prudent thing to do, was just push it to the people who needed to get it.”

“We did communicate that information in a timely fashion to the Capitol Police and (Metropolitan Police Department) in not one, not two, but three different ways,” Wray said, though he added that since the violence that ensued was “not an acceptable result,” the FBI was looking into what it could have done differently.