Brian Laundrie, the sole person of interest in the murder of Gabby Petito, died from a gunshot wound to the head, a family lawyer told news organisations on Monday.
A forensic anthropologist declared the cause of death to be suicide, lawyer Steve Bertolino said.
“Chris and Roberta Laundrie have been informed that the cause of death was a gunshot wound to the head and the manner of death was suicide,” Mr Bertolino told The New York Post.
“Chris and Roberta are still mourning the loss of their son and are hopeful that these findings bring closure to both families.”
Law enforcement officials last month concluded that remains found in a Florida wilderness park were Laundrie's after analysing the dental records.
A search that enlisted the help of US federal, state and local authorities took place in September, two weeks after Laundrie disappeared from his parents' home in North Port, Florida.
Suspicion arose when he returned home alone after a trip he took with Petito, his fiancée, and after police body cam footage surfaced implying the couple had a domestic dispute while on the road.
The couple had embarked on a cross-country adventure in July. Petito had quit her job and decided to document their journey on social media.
She posted her final photo to Instagram on August 25, the same day she last spoke to her mother by phone.
A coroner last month determined Petito had been killed by strangulation and ruled her death a homicide.
Laundrie was declared a “person of interest” in the case but was never charged in her death. The investigation continues.
Petito was last seen alive on August 26. Her body was discovered in September near a remote campground in western Wyoming.
The traveller's disappearance became an internet sensation that grew more enigmatic by the day.
It also renewed the debate over the disproportionate attention afforded to missing white women versus women of colour in the US.