Greg Gianforte told an officer that Guardian newspaper reporter Ben Jacobs had grabbed him by the wrist and pulled him to the floor of his campaign office after “interrogating” him, according to notes from a Gallatin County sheriff’s officer who interviewed the politician after the incident unfolded.
He also claimed that the “liberal media” was “trying to make a story” out of the altercation that took place just a day before his victory in a 25 May special election.
Multiple witnesses came forward to contradict Gianforte’s account, however, and the politician has since pleaded guilty to misdemeanour assault.
More than 100 pages of documents, photos and audio gathered over the course of the investigation were released under a court order after requests from a number of news organisations.
The documents include interviews with members of a Fox News crew who were in the room when the attack unfolded. They said Gianforte had been angry over what he perceived as biased coverage and body-slammed Mr Jacobs onto the ground before punching him.
One of the congressman’s staffers, Josh Elle, who worked as Gianforte’s driver, told officers that he had been in an adjacent room when he heard a commotion.
When he peered into the other room, he said he was Gianforte striking the journalist with closed fists before someone else in the room closed the door.
Another worker said Gianforte and others involved with the campaign had been complaining earlier on in the day about “duplicitous” coverage by the Guardian and Buzzfeed.
In his initial description of the altercation, Gianforte had told Sergeant Scott Secor that Mr Jacobs had approached him while he was preparing for an interview with Fox News and “started interrogating in a very intensive way”.
“I probably shouldn’t do it, but I reached out for his phone,” Gianforte said. “He grabbed my wrist, he spun and we ended up on the floor ... so he pulled me down on top of him,” the sergeant quoted the politician as saying.
Hours after the assault, Gianforte’s campaign spokesman, Shane Scanlon, also issued a statement that blamed the attack on the reporter, claiming Mr Jacobs had grabbed the candidate’s wrist.
Gianforte has issued a public apology to Mr Jacobs and told supporters he wasn’t proud of his actions.
His spokesman, Travis Hall, insisted on Friday that the documents revealed “nothing new”.
“No one was misled, and anyone who says otherwise is mistaken.
“Greg took responsibility for his actions and is focused on serving the people of Montana,” he said in a statement emailed to AP.
Since pleading guilty to the assault, Gianforte has been forced to pay a $385 fine and complete 40 hours of community service, as well as 20 hours of anger management counselling.
He has also donated $50,000 (£44,000) to the Committee to Protect Journalists.
Gallatin County Attorney Marty Lambert said that while he was aware of the Republican’s comments to investigators, additional charges, such as obstruction of justice, were not considered as authorities were focused specifically on the assault allegation.
“When the police are investigating a case, suspects of crimes will say misleading things, and apparently that’s exactly what happened here on the part of both Mr Gianforte and his campaign,” Mr Lambert said.
“It is not a crime per se to lie to the cops,” he continued. “The main thing here is he was charged with assaulting Ben Jacobs and pled guilty to that.”
The politician is up for re-election next year and has filed an official bid to run, with six Democrats entering the race to challenge him.
Additional reporting by AP