"I have chills right now," Nina Celie Angelo told Fox News.
"It's crazy because it wasn't just like we passed them on the street — it was a full-blown incident."
Angelo may have been one of the last people to see Gabby Petito alive and what she saw offers a chilling insight into the toxic relationship the 22-year-old endured with 23-year-old Brian Laundrie.
Now authorities have confirmed that Petito was killed - and Laundrie is missing.
Angelo told Fox News she and her boyfriend Matthew England were in Jackson Hole, Wyoming, in late August to attend a wedding.
They were dining at a Tex-Mex restaurant called Merry Piglets, between 1 and 2pm on August 27, when they claim to have seen an "aggressive" Laundrie arguing with a waitress.
Angelo said she couldn't hear the details of the conversation but believed the row centred on paying the bill.
She recounted how Laundrie's behaviour left Petito in tears, desperately trying to apologise for her boyfriend, who stormed in and out of the restaurant several times.
"It looked as though they were like almost getting kicked out," Angelo told ABC News.
"It wasn't necessarily between them, it was more so Gabby abruptly leaving the restaurant crying, and Brian was just evidently really upset, pissed off, I would say. I would say Gabby was upset, he was angry, and he was just being very temperamental towards the restaurant staff."
Angelo's boyfriend Matthew England told Fox he had reported the encounter to the FBI.
The tense scenes erupted two days after Petito's final Instagram post and roughly two weeks after a witness called police about a fight between Petito and Laundrie in Moab, Utah.
Angelo and England said when they saw the police bodycam video of the Moab incident, they recognised the couple immediately.
Laundrie was also wearing clothes England said he recognised from their encounter and "looked kind of like he had been living out in a van for a little while".
"I spent the last three or four days really kind of racking my brain," he told Fox News. "And I woke up this morning and went to Facebook, and there was that video with the police on it, right away. That was the couple."
"I would bet $10 million, I'm 1000 per cent sure that was him and that was her," he said.
August 27, the day of the alleged restaurant incident, is the last time that Petito's family heard from her.
Two days later, a woman claims she gave Laundrie a ride.
He told her he had been camping by himself while Petito worked on social media posts from their van.
"Her account is plausible, it appears," police spokesperson Josh Taylor said.
On September 1, Laundie returned home to Florida, alone.
Ten days later, Petito's family reported her missing.
Laundrie later disappeared and then authorities found Petito's body in a remote Wyoming location, ruling her death a homicide.