The cause of death came from an anthropologist who received Laundrie's remains after an autopsy by the Sarasota County medical examiner did not produce concrete results.
"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," Bertolino said. "Chris and Roberta are still mourning the loss of their son and are hopeful that these findings bring closure to both families."
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Petito, 22, was discovered slain in September on the edge of Grand Teton National Park in Wyoming, one of the places the young couple had visited on the trip they documented through social media videos.
The case garnered national attention as police and the families initially sought Petito and then Laundrie as well after his disappearance.
An autopsy in Wyoming concluded Petito died by strangulation and that it was a homicide.
Laundrie, 23, was listed as a "person of interest" in her killing but he was charged only with fraudulent use of a debit card.
His remains were found in a nature preserve not far from his family's home in North Port, Florida, where both he and Petito had been living.
Both were originally from Blue Point on Long Island.
Laundrie returned home alone Sept. 1 from his trip with Petito.
Her body was found Sept. 19 in the Wyoming park and authorities say it had been there for about a month.
Laundrie told his parents Sept. 13 he was headed to the Carlton Reserve Park in Florida.
That was the last publicly known contact anyone had with him.
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The couple first met as teenagers but gained an online following while on their trip in a converted Ford Transit van in videos filled with happy scenes that may have concealed deeper problems.
After Petito disappeared, the case became a true-crime obsession on social media.
The couple was stopped Aug. 12 by police in Utah after they had a physical altercation, but no domestic violence charges were filed.
WATCH: Tracking the Gabby Petito disappearance
The video above is a part of TRACKING, a digital video series from ABC News that uses social media, public records, mapping and expert analysis to piece together timelines of how major news events transpired. Watch more ABC News originals here.
If you or someone you know is in emotional distress or considering suicide, call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255).