Brian Laundrie Update: This 'Clue’ Could Prove Who Killed Gabby Petito

Investigators are now looking for other clues to determine who killed 22-year-old Gabby Petito after authorities found Brian Laundrie, the sole person of interest in her murder, dead last week.

Paul Belli, a retired lieutenant of the Sacramento County Sheriff’s Office and president of the International Homicide Investigators Association, believes the killer could have left DNA on Petito when she was manually strangled to death. However, he did note that DNA review could get more difficult if the person of interest is someone the victim was involved with.

"You would expect DNA on either one of them from the other," Belli told CNN. "But I mean, if there's DNA maybe where it shouldn't be, that could be kind of a clue as to what may have occurred.

"So there are ways to absolutely, at least get you to a point where you're like, 'OK, this definitely makes sense, this is the person who did this crime.'"

Petito, whose body was found in Wyoming’s Grand Teton National Park on Sept. 19, died of homicide by manual strangulation or throttling, according to a final autopsy report from Teton County Coroner Dr. Brent Blue.

Little is known about the events that led up to her death. Publicly available information said Laundrie returned home alone to North Port, Florida in Petito’s vehicle on Sept. 1 amid their cross-country trip. Petito’s family reported her missing on Sept. 11, while Laundrie’s family said he disappeared on Sept. 13 after going out for a hike at nearby Carlton Reserve.

Authorities launched a month-long manhunt for Laundrie, who the FBI named as the sole person of interest in the murder of Petito. He had also been issued an arrest warrant for illegally using Petito’s card to make a purchase or withdrawal of more than $1,000 between Aug. 30 and Sept. 1.

Laundrie’s skeletal remains were discovered in the Myakkahatchee Creek Environmental Park on Oct. 20. His body was found alongside personal items, such as a backpack and a notebook. Investigators also found clothing items that were consistent with what Laundrie was believed to be wearing when he took off on Sept. 13, according to The Hill.

An autopsy of Laundrie’s body came back inconclusive. His remains have been sent to an anthropologist to help determine the time and manner of his death.