The US attorney general, Merrick Garland, on Wednesday vowed that the justice department would hold accountable all those responsible for the deadly 6 January attack, whether they were physically present at the Capitol or not.

Garland’s remarks come as he faces growing calls from lawmakers, legal experts and former elected officials to intensify the department’s investigation into the events of Capitol assault, and in particular to prosecute those who helped orchestrate the failed attempt to overturn the 2020 election results, including Donald Trump and his associates.

In a solemn speech on the eve of the first anniversary of the assault on the seat of government, Garland said it did not matter whether the perpetrators had been present at the Capitol riot or committed other crimes that wrought chaos on that day.

“The justice department remains committed to holding all January 6th perpetrators, at any level, accountable under law – whether they were present that day or were otherwise criminally responsible for the assault on our democracy,” Garland said in his address, delivered from the justice department’s Great Hall in Washington. “We will follow the facts wherever they lead.”

Garland recounted in detail the brutality of the day, contesting a rightwing revisionist narrative that the attack was not violent. Officers had been assaulted with pipes and poles, beaten and shocked with stun guns, he said. One officer had been dragged down the stairs by rioters, while lawmakers and the vice-president fled for their lives.

“As a consequence, proceedings in both chambers were disrupted for hours – interfering with a fundamental element of American democracy: the peaceful transfer of power from one administration to the next,” he said. “Those involved must be held accountable, and there is no higher priority for us at the Department of Justice.”

Garland did not mention Trump by name, and in keeping with the justice department’s longstanding rule not to comment on ongoing investigations, he did not detail any possible leads the department was pursuing related to the former US president, his family or his allies.

But the carefully crafted speech seemed designed to address concerns about the focus of the investigation. Garland said he understood the intense public interest in the case and promised that the actions taken by the department so far “will not be our last”.

The department’s work so far, he explained, was laying the foundation for more serious and complicated cases. “In complex cases, initial charges are often less severe than later charged offenses,” he said. “This is purposeful as investigators methodically collect and sift through more evidence.

“There cannot be different rules for the powerful and the powerless,” he added.

The investigation into the events of 6 January was one of the “largest, most complex and most resource-intensive investigations” in the nation’s history, Garland said.

To date, he said, investigators had issued 5,000 subpoenas and search warrants, seized 2,000 devices, viewed 20,000 hours of video footage, searched 15 terabytes of data and received 300,000 tips from the public. More than 700 people in nearly all 50 states and the District of Columbia have been charged for their roles in the insurrection, which left 140 law enforcement officers injured. Five officers who defended the Capitol that day have since died.

Reading their names aloud, Garland asked for a moment of silence to remember the fallen officers.

On Thursday, Democratic leaders in Congress will host a day of remembrance events, beginning with speeches from Joe Biden and Kamala Harris at the US Capitol.

Previewing his speech, the White House press secretary, Jen Psaki, said Biden would acknowledge “the singular responsibility President Trump has for the chaos and carnage” of 6 January.

“The president is going to speak to the truth of what happened, not the lies that some have spread since, and the peril it posed to the rule of law and our system of democratic governance,” Psaki said, adding that Biden was “clear-eyed about the threat the former president represents to our democracy and how the former president constantly works to undermine basic American values and rule of law”.

Garland’s remarks extended beyond the events of 6 January. He lamented a rise in violence that has touched nearly every aspect of American life. He pointed to attacks on elections officials, airline crews, teachers, journalists, police officers, judges and members of Congress.

“These acts and threats of violence are not associated with any one set of partisan or ideological views,” he warned. “But they are permeating so many parts of our national life that they risk becoming normalized and routine if we do not stop them.”

The justice department, he promised, would work within the bounds of the first amendment to prosecute all those who made unlawful threats. He also committed the department to using “the enforcement powers we have” to protect voting rights, warning of efforts in some states to audit election results, drive out election officials or allow state lawmakers to overturn the will of voters.

“As with violence and threats of violence, the justice department – even the Congress – cannot alone defend the right to vote,” he said. “The responsibility to preserve democracy – and to maintain faith in the legitimacy of its essential processes – lies with every elected official and every American.”