The partner of Capitol police officer Brian Sicknick, who died after the January 6 attack on Congress, has sued Donald Trump alleging that the former president’s “campaign of lies and incendiary rhetoric” about the 2020 presidential election motivated the mob and played a “significant role in the medical condition” that killed the officer.

The lawsuit, filed in Washington DC federal court, names Trump and two other January 6 rioters who attacked Sicknick, and demands millions in damages. It was brought by Sicknick’s longtime partner, Sandra Garza, one day before the insurrection’s second anniversary.

Garza alleges that Trump’s months-long refusal to recognize Joe Biden’s win spurred violence that proved fatal to Sicknick. “Many participants in the attack have since revealed that they were acting on what they believed to be Defendant Trump’s direct orders in service of their country,” the lawsuit states.

It added that Trump’s speech hours before the riot, urging people to “fight like hell”, was “the culmination of a coordinated effort to subvert the certification vote”.

“Trump directly incited the violence at the US Capitol that followed and then watched approvingly as the building was overrun,” the lawsuit states. “Trump did all these things solely in his personal capacity for his own personal benefit and/or his own partisan aims.”

The other two defendants are rioters Julian Khater and George Tanios, who were among those “engaged in a confrontation” with the police, including Sicknick, assigned to guard the Capitol’s Lower West Terrace. The rioters tore down barriers, and assaulted officers with hands, feet, and “other objects”, the lawsuit alleges.

It says Khater blasted bear spray in Sicknick’s face, after Tanios brought the spray with him. As Sicknick turned back, “incapacitated by the bear spray”, Khater kept spraying and continued forward, spraying at least two other officers.

Sicknick, who remained at the Capitol late into the evening, collapsed at about 10pm. Paramedics rushed him to hospital but he died less than 24 hours later.

Washington DC’s medical examiner determined that Sicknick died of “natural causes – specifically, a series of strokes.” But the examiner emphasized that “all that transpired on [January 6] played a role in his condition”.

The lawsuit argues that Trump knew chaos and violence could grow from his “stop the steal” rhetoric. “The horrific events of January 6, 2021, including Officer Sicknick’s tragic, wrongful death, were a direct and foreseeable consequence of the Defendants’ unlawful actions,” the suit says.

“Trump was aware that his actions prior to and on January 6, 2021 promoted and encouraged the mob to violently storm the US Capitol.”

It added: “Officer Sicknick’s death was a reasonable and foreseeable consequence of Defendants’ intentional words and actions.”

The suit also cites the findings of the House January 6 committee, which accused Trump of a “multi-party conspiracy” to derail certification of the election. The committee unanimously made four criminal referrals to the US justice department against Trump for his role in the insurrection, the first time Congress has taken such a step against a former president.

Trump’s attorney did not immediately respond to a request for comment.

Both Tanios and Khater were arrested after the riot and pleaded guilty, Tanios to entering and remaining in a restricted building and Khater to assaulting officers with a dangerous weapon.

Beth Gross, Tanios’s attorney, said in a statement that “the recent civil lawsuit naming him as a defendant veers well beyond what the facts support and misconstrues Mr Tanios’s actual conduct”.