Costa Rican authorities have confirmed once and for all that Brett Gardner’s son Miller died from carbon monoxide inhalation during a family vacation.

Mystery has surrounded the 14-year-old’s death since it was announced two weeks ago, with asphyxiation and food poisoning both ruled out by examiners, and the hotel denying claims carbon monoxide poisoning was the cause.

Now, though, the official toxicology report has been released, confirming that Miller passed away as a result of exposure to carbon monoxide, after a saturation level of 64% was found in his room.

The report, released by Randall Zuniga – general director of the OIJ – late on Wednesday, added that ‘concentrations above 50% are already lethal.’

He added: ‘In this case, the saturation percentage is higher, thus proving the police’s hypothesis that the death was due to exposure to carbon monoxide.’

Zuniga also confirmed that the case has now officially been closed, and revealed that tests for other drugs had also returned negative results.

Miller Gardner (second right) died suddenly while on a vacation with dad Brett (right), mom Jessica (second left) and older brother Hunter, 16 (left) 

His body was found in his room at the Arenas Del Mar Beachfront & Rainforest Resort 

He explained: ‘Other drug tests were conducted, including fentanyl and other substances; all were negative.’

The next step, as the Gardner family await the green light to bring Miller’s body back to the US, is for the OIJ to send the toxicology report to the Department of Forensic Medicine, per local reports. 

On Tuesday, the cause of death had remained shrouded in mystery after a spokesperson for the Arenas Del Mar Beachfront & Rainforest Resort – where the Gardners were staying – adamantly denied the police’s findings.

‘The levels in the hotel room were non-existent and non-lethal. There was an error in this initial reporting,’ a spokesperson for the resort told the New York Post. 

The police had initially reported ‘high levels of carbon monoxide contamination’ in the hotel room, but were awaiting confirmation from the toxicology reports.

The hotel, meanwhile, said that the carbon monoxide levels were detected in a ‘mechanical room that guests do not occupy,’ rather than the guest room itself. 

The Gardners’ guest room was closed off ‘out of an abundance of caution’ as they ‘await for conclusive results to confirm the cause of this unfortunate death,’ Arenas Del Mar added.

Brett Gardner’s son Miller, 14, died suddenly while on vacation in Costa Rica on March 21

Randall Zúñiga, general director of Costa Rica’s Judicial Investigative Agency, confirmed the toxicology report on Wednesday and said the case has now been closed

The high-end resort, where reservations cost as much as $1,300 per night, has reportedly slashed its prices with its top-end rooms now said to be listed for $998. 

Miller was discovered not breathing in his room on March 21 while on a trip with the rest of the Gardner family in the Central American country.

The tragedy happened after Brett, a former World Series winner with the Yankees, Jessica, Miller and older son Hunter, 16, all suffered severe stomach cramps, vomiting and diarrhea following dinner at an outside restaurant the night before.

Desperate medics battled in vain for 30 minutes to try to kickstart 14-year-old Miller’s heart after he was found by a frantic family member who raised the alarm, DailyMail.com exclusively revealed.

Brett and wife Jessica shared a heartbreaking tribute to their late son in an emotional obituary Monday.

‘The void Miller’s passing leaves in the hearts of his family, friends, teammates, teachers, coaches and others will be felt for years,’ the family wrote.

The tragedy happened after Brett, Jessica, Miller and older son Hunter, 16, all suffered severe stomach cramps, vomiting and diarrhea after dinner at an outside restaurant the night before

The Arenas Del Mar Beachfront & Rainforest Resort initially denied the police findings

‘The Gardner family will forever cherish the places they visited, the people they met, the friends they made, and the memories they created together.

‘Miller’s time here with them was brief but his spirit will carry on forever through those who were impacted by the way he lived.’

The family revealed that they would be honoring Miller’s legacy by using his memory to help benefit other children, requesting donations to be made to the Make-A-Wish Foundation.

‘Miller was so blessed with experiences and friendships in his 14 years, and he would want other children to have the opportunity to create their own wonderful memories,’ the obituary continued.

A private celebration of life will be held for Miller (pictured) at an undisclosed later date

Dad Brett spent his entire Major League Baseball career as an outfielder with the Yankees

The heart-wrenching statement also remembered Miller’s active participation in school and the community, recalling his role on both the middle school football team and junior varsity baseball team and place on the Honor Roll amid his multitude of hobbies.

Miller was described as a fan of playing golf, fishing, hunting, riding dirt bikes, and traveling to new places with his family.

‘In this time of unimaginable loss, the family prays that joy and healing will come to others who share their grief,’ the obituary concluded.

A private celebration of life will be held for Miller at an undisclosed later date. The service will be reserved for family and close friends.