Ellen Chung, 31, Jonathan Gerrish, 45, their daughter Miju, 1, and their dog Oski were found dead along a hiking trail in the Sierra National Forest on Aug. 17.
After a lengthy investigation into their cause of death — which remained a mystery for months — the Mariposa County Sheriff's Office announced in October that the family died from hyperthermia and probable dehydration. Their dog, 8, also suffered a heat-related death.
According to the investigative records recently obtained by several outlets, experts believe that the couple likely died while trying to save their daughter and themselves.
"All the evidence kept pointing back to heat exposure and lack of water," investigators said in records released to The San Francisco Chronicle under California public records laws.
The temperature was 76 degrees on Aug. 15, the alleged day of their hike, but later peaked at 109 — and investigators said ground temperatures would likely have been higher due to a lack of shade, The Chronicle reported.
Ellen chung/ instagram Ellen Chung and John Gerrish
One expert interviewed by detectives suggested the family overheated, causing their brains and organs to shut down, per The Chronicle.
A survival expert reportedly concluded that heat as well as the terrain on the trail led to their deaths — and that "it is likely" their daughter's health began to deteriorate first.
"Sadly, I believe they were caught off guard, and once they realized their situation, they died trying to save their child and each other," the survival trainer wrote in an email to detectives, according to the outlet.
The Mariposa County Sheriff's Office didn't immediately return PEOPLE's request for comment about the expert opinions.
Rosanna Heaslett John Gerrish, Ellen Chung and daughter Muji
"A suffering infant would give two parents the drive to push through the extreme heat," the survival trainer added in the message, according to local ABC channel KABC, which also obtained the investigative reports.
"When one could no longer continue, they stayed behind to care for the child and pet, while the other tried to forge on and get help for their loved ones," the expert wrote, per the outlet. "It is a tragedy of the highest order."
A Modesto doctor who works with extreme heat victims told investigators that individuals can die within a couple of hours of having a heatstroke, The Chronicle reported.
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The bodies of the family were found on the morning of Aug. 17, one day after they were reported missing by their babysitter, PEOPLE previously reported.
The Chronicle reported that the bodies of Gerrish, Miju and Oski were located "on a series of steep switchbacks of the Savage Lundy Trail." A Ford key fob was also found about 100 feet below where Gerrish was found.
Courtesy Steven Jeffe John Gerrish, Ellen Chung
Chung's body was found about an hour later in an area about 13 feet higher than her other family members.
Among the items found in her backpack was a 2.5-liter water bladder, which detectives said had only a "few remaining drops" of water left inside.
A Forest Service employee familiar with the trail told investigators that locals typically "stay clear" of the area in the summer, according to The Chronicle.
Police previously noted that hyperthermia deaths are "rare" for Mariposa County.
"This is the first hyperthermia cause of death that I've witnessed here in 20 years," Sheriff Jeremy Briese said in October as the family's cause of death was revealed.
In a statement read by police at the press conference, loved ones said that the loss of the couple, their daughter and their dog was "indescribable."
"Our hearts will never forget the beautiful lives of John, Ellen, Miju and of course, Oski," they said in the statement. "They will remain with us wherever we are and whatever we do."