WASHINGTON — When an oil-field worker named Guy Wesley Reffitt returned to Texas after taking part in the attack on the Capitol last year, his welcome home was not entirely warm.
He bragged to his family about confronting the police outside the building and promised that the violence there was only “the beginning,” according to federal prosecutors. His 18-year-old son pushed back, accusing him of having broken the law.
A few days later, Mr. Reffitt realized his son might be right and that the F.B.I. might in fact be on to him. In a burst of anger, he threatened his son and daughter, telling them that they would face his wrath if they sold him out to the authorities.
On Thursday, the son, Jackson Reffitt, faced his father from the witness stand in Federal District Court in Washington, testifying against him in a remarkable tableau that captured the painful rupture in one family — and in some ways the nation — caused by the events of Jan. 6, 2021.
“He said, ‘If you turn me in, you’re a traitor,’” Jackson Reffitt told the jury as his father watched him intently from across the courtroom and then looked down. “‘And traitors get shot.’”
The older Mr. Reffitt, 41, is the first defendant out of more than 700 to go on trial in connection with the Capitol attack, and in the past two days the prosecution has documented how he drove to Washington with a fellow member of a Texas militia and, armed with a pistol, led a pro-Trump mob in an advance on the police outside the building.
But with the appearance of his son on the witness stand, the trial took an unusually personal — and emotional — turn.
Testifying for more than three hours, Jackson Reffitt, now 19, told the jury how his father had become more distant and severe in his beliefs in 2016, the same year Donald J. Trump was elected president. Father and son, he said, did not see eye-to-eye on politics.
“I was moderately left and my father was moderately right,” the younger Mr. Reffitt said, adding that during that election year, “we both went further in our own direction.”
Jackson Reffitt also said his father was a member of the Texas Three Percenters, a state militia group closely linked to the gun rights movement. Guy Reffitt flew a flag outside the family’s home in Wylie, Texas, emblazoned with a Three Percenters’ logo. His son told the jury that he often went about his business with a .40-caliber pistol on his hip.
Things became more tense between the father and son in December 2020, Jackson Reffitt said, as Mr. Trump was undertaking multiple, overlapping schemes to reverse his election defeat. Much of the conflict played out on a family group chat, several messages of which were shown to the jury Thursday.
“Congress has made fatal mistakes this time,” Guy Reffitt wrote on Dec. 21 that year. “This isn’t about Trump, it’s much much bigger. It’s about OUR country.”
The son wrote back: “I don’t think Congress makes up all 80,000,000 votes for biden but okkk.”
The father then responded: “It’s not about Trump. Or Biden. What comes next is about tyranny. Hold my beer and I’ll show you.”
Reading these and similar messages — some about his father traveling to Washington for Jan. 6 — was “scary and surreal,” Jackson Reffitt said.
He told the jury that he was worried about what his father might do. So one day that month, he Googled “F.B.I.” and “tip” and followed the link to an online bureau tip line, describing what had passed between him and his father.
He testified that he was ashamed for having reached out to the F.B.I. “I just felt gross,” he explained.
But the F.B.I. did not respond for weeks, and on Jan. 6, 2021, Jackson woke up at his girlfriend’s house to find a text on the family group chat, indicating that his father was in Washington. He told the jury that he hurried home and found his mother and sisters watching the chaos at the Capitol unfolding on TV.
Capitol Riot’s Aftermath: Key Developments
The potential case against Trump. In a court filing, the House committee investigating the Jan. 6 attack said there was enough evidence to conclude that former President Donald J. Trump and some of his allies may have engaged in a criminal conspiracy as he fought to remain in office.
“I kind of just stood there in awe and disappointment, saddened and scared,” he said.
Two days later, as Guy Reffitt headed back from Washington, he sent his family a text that seemed to celebrate the violence he took part in.
“Shot multiple times with clay balls and Pepper Sprayed heavily,” he wrote. “We took the United States Capital. We are the Republic of the People.”
“Yeah,” his son responded, “you know they are tracking down everyone who was there right?”
“Yep, don’t care,” his father answered. “I broke no laws.”
The father and son had a similar conversation when Guy Reffitt finally got back to the family’s home in Wylie. A few days later, his father made the threat about “traitors,” Jackson Reffitt said. Jackson met with the F.B.I. that day. His father was arrested within a week.
Testimony at the trial earlier in the day was not quite as dramatic and was largely given over to the evidence that investigators had extracted from Mr. Reffitt’s electronics devices, including a 30-minute video he made of himself in the crowd outside the Capitol with a camera mounted on his helmet.
In the video, a foul-mouthed Mr. Reffitt can be heard repeatedly urging people in the mob to storm into the building and drag the lawmakers, including Speaker Nancy Pelosi, out by their hair or ankles.
“I didn’t come here to play — I’m taking the Capitol,” he said at one point. “I just want to see Pelosi’s head hitting every stair on the way out.”
Prosecutors also showed the jury a recording of a Zoom call that Mr. Reffitt took part in with other members of the Texas Three Percenters after he returned from Washington. The call contained an echo of the testimony given Wednesday by a former Capitol Police officer, Shauni Kerkhoff. Ms. Kerkhoff told the jury that she had started to panic after firing dozens of pepper balls at Mr. Reffitt, none of which managed to stop his advance up a staircase at the building.
On the Zoom call, Mr. Reffitt recounted the same events, telling his fellow militiamen that he had been hit at least 20 times by Ms. Kerkhoff’s projectiles, but that his body armor had absorbed most of the blows.
“I said, ‘Baby, you’re going to need a bigger gun than that,’” he said on the call, adding, “They’re lucky we didn’t shoot them.”