An FBI behavioral analyst claims that the day Brian Laundrie and Gabby Petito argued in a Wyoming restaurant on Aug. 27 may be the key to the latter's tragic fate. 

The 22-year-old YouTuber was seen having an explosive argument between her fiancé and a worker at a Jackson Hole restaurant called Merry Piglets witnessed the entire thing. 

Dr. Ann Wolbert Burgess, the person who pioneered the FBI's Behavioral Science Unit, said that the restaurant incident was "the second and most important" event before Petito's death that raised some serious red flags. 

The other significant incident, which showed that Petito and Laundrie had serious issues in their relationship and some danger in the latter's actions, was the domestic dispute that was called in on Aug. 12 in Utah. 

The expert told Fox News of the incident at Merry Piglets, "How she has to apologize for his behavior is something that's kind of characteristic, and this probably enrages him even more because he wants to appear in a certain way."

Witness Nina Celie Angelo, who witnessed the incident at the time, said last month that she couldn't hear the conversation but believed that Laundrie was arguing with a restaurant employee over the bill or the money. 

Angelo described Laundrie's body language as "aggressive" and even added that the 23-year-old left and returned about four times. 

At one point, Petito reportedly came inside and apologized for her boyfriend's behavior, per the witness. 

Gabby Petito Cause of Death

A few days ago, the Teton County Coroner Brent Blue publicized that Gabby Petito's cause of death was strangulation.

He claimed that she may have been dead three to four weeks before her body was discovered on Sept. 19. 

So the date of Petito's death is between Aug. 27 and Aug. 30, a few days after Laundrie returned home alone to his North Port, Florida home in the van they shared during their cross-country road trip. 

READ ALSO: Brian Laundrie Plea Deal: Social Media Weighs In The Possible Punishment He Deserves If Proven Guilty

Brian Laundrie Still Missing and On The Run

With Halloween just around the corner, internet sleuths believe that Brian Laundrie may use the holiday to disguise himself in a costume and make a getaway. 

In a Facebook group dedicated to the case, a poster said, "So Halloween is coming up." 

"Is anyone concerned that this will make it extremely easy for [Brian] to make a getaway to wherever he needs to go?"

"Imagine him just walking down the street in costume on Halloween."

READ MORE: Brian Laundrie Found But FBI Witholding Proof and Location Details?